for examples , we offer prime brokerage services , including capital introduction and securities lending to hedge funds ; and our model portfolio technology and automated share allocation and rebalancing tools are particularly attractive to financial advisors . we provide a host of analytical tools such as the probability lab sm , which allows our customers to analyze option strategies under various market assumptions . the ib investors ' marketplace sm allows wealth advisors to search for money managers and assign them to client accounts based on their investment strategy . ib employeetrack sm is widely used by compliance officers of financial institutions to streamline the process of tracking their employees ' brokerage activities . portfolio builder allows our customers to set up an investment strategy based on research and rankings from top buy-side providers and fundamental data . in addition , ria compliance center provides information to assist advisors with registration and compliance obligations . market making . we conduct our market making business primarily through our th subsidiaries . as one of the largest market makers on many of the world 's leading exchanges , we provide liquidity by offering competitively tight bid/offer spreads over a broad base of over one million tradable , exchange-listed products . as principal , we commit our own capital and derive revenues or incur losses from the difference between the price paid when securities are bought and the price received when those securities are sold . because we provide continuous bid and offer quotations and we are continuously both buying and selling quoted securities , we may have either a long or a short position in a particular product at a given point in time . our entire portfolio is evaluated each second and continuously rebalanced throughout the trading day , thus minimizing the risk of our portfolio at all times . this real-time rebalancing of our portfolio , together with our real-time proprietary risk management system , enables us to curtail risk and to be profitable in both up-market and down-market scenarios . in the past several years our market making business has suffered from competitive pressures and along with the rapid increase of our electronic brokerage business , its significance has diminished . the operating business segments are supported by our corporate segment which provides centralized services and executes our currency diversification strategy . business environment the operating environment for our brokerage business continued to exhibit positive trends in 2015. investor uncertainty accompanied a downdraft in the equity markets in the third quarter of 2015 , and a period of increased volatility led to a contraction of margin borrowings but higher trading volumes . we maintained our position as the largest u.s. electronic broker as measured by number of customer revenue trades , which increased 14 % over the prior year , driving a 12 % increase in commissions and execution fees . new customer account growth continued to gain momentum as total customer accounts increased 18 % to 331 thousand in 2015. institutional customers , such as hedge funds , mutual funds , introducing brokers , proprietary trading groups and financial advisors , comprised approximately 44 % of total accounts and approximately 64 % of total customer equity at the end of 2015. our customer base continues to be geographically diversified , as our customers reside in over 190 countries and over 50 % of new customers came from outside the u.s. average equity per account increased by 1 % , to $ 204 thousand as of december 31 , 2015 . 45 customers continued to take advantage of our low margin lending rates , which are tied to benchmark rates , such as the federal funds rate in the u.s. in 2015 , our customers paid 0.5 % to 1.86 % for their u.s. dollar margin loans with us . after building steadily for a number of years , customer margin loans increased by only 1 % from 2014 , as customers responded to the volatile markets by reducing their leverage . in spite of the modest growth in customer margin loans , electronic brokerage net interest income grew 24 % in 2015 , because average customer credit balances and margin loans for the year were up 18 % and 10 % , respectively . market making segment results increased in 2015 driven by higher market volatility and periods of higher trading activity . the following is a summary of the key profit drivers that affect our business and how they compared to the prior year : global trading volumes . according to data received from exchanges worldwide , volumes in exchange-listed equity-based options increased by approximately 10 % globally and decreased 3 % in the u.s. for the year ended december 31 , 2015 , compared to 2014. during 2015 ( 2014 ) we accounted for approximately 7.8 % ( 8.5 % ) of the exchange-listed equity-based options ( including options on etfs and stock index products ) volume traded worldwide and approximately 11.3 % ( 11.2 % ) of exchange-listed equity-based options volume traded in the u.s. it is important to note that this metric is not directly correlated with our profits . see the tables on pages 59-60 of this annual report on form 10-k for additional details regarding our trade volumes , contract and share volumes and brokerage statistics . volatility . our market making profits are generally correlated with market volatility since we typically maintain an overall long volatility position , which protects us against a severe market dislocation in either direction . based on the chicago board options exchange volatility index ( `` vix® `` ) , the average volatility increased to 16.7 in 2015 , an increase of 18 % from the average of 14.2 in 2014. the ratio of actual to implied volatility is also meaningful to our results . story_separator_special_tag additional consolidation among market centers may adversely affect the value of our smart routing software . a driver of our market making profits is the relationship between actual and implied volatility in the equities markets . the cost of maintaining our conservative risk profile is based on implied volatility , while our profitability , in part , is based on actual volatility . hence , our profitability is increased when actual volatility runs above implied volatility and it is decreased when actual volatility falls below implied volatility . implied volatility tends to lag actual volatility . see `` risk factors `` in part i , item 1a of this annual report on form 10-k for a discussion of other risks that may affect our financial condition and results of operations . 51 results of operations the tables in the period comparisons below provide summaries of our consolidated results of operations . the period-to-period comparisons below of financial results are not necessarily indicative of future results . replace_table_token_10_th 52 the following table sets forth our consolidated results of operations as a percent of our total net revenues for the indicated periods : replace_table_token_11_th year ended december 31 , 2015 ( `` current year `` ) compared to the year ended december 31 , 2014 ( `` prior year `` ) net revenues total net revenues , for the current year , increased $ 146 million , or 14 % , to $ 1,189 million , compared to the prior year . the increase in net revenues was primarily due to higher commissions and execution fees and net interest income . trading volume is an important driver of revenues and costs for both our electronic brokerage and market making segments . during the current year , our futures contract and stock share volumes increased 14 % and 12 % , respectively , while options contract volume remained unchanged , compared to the prior year . trading gains trading gains , for the current year , increased $ 8 million , or 3 % , to $ 269 million , compared to the prior year . as market makers , we provide liquidity by buying from sellers and selling to buyers . during the current year , our market making operations executed 65.9 million trades , an increase of 2 % compared to the number of trades executed in the prior year . market making stock share volume increased 28 % , while options and futures contract volumes decreased 3 % and 4 % , respectively , compared to the prior year . 53 trading gains were favorably impacted by higher volatility levels and periods of higher trading activity . the vix® , which measures perceived u.s. equity market volatility , increased 18 % to an average of 16.7 for the current year , compared to an average of 14.2 for the prior year . the ratio of actual to implied volatility increased to an average of 88 % for the current year , compared to an average of 79 % for the prior year . included in trading gains are net dividends . dividend income and expense arise from holding market making positions over dates on which dividends are paid to shareholders of record . when a stock pays a dividend , its market price is generally adjusted downward to reflect the value paid , which will not be received by those who purchase stock after the ex-dividend date . hence , the apparent gains and losses due to these price changes , reflecting the value of dividends paid to shareholders , must be taken together with the dividends paid and received , respectively , to accurately reflect the results of our market making operations . commissions and execution fees commissions and execution fees , for the current year , increased $ 68 million , or 12 % , to $ 617 million , compared to the prior year , driven by continued customer account growth and increased customer trading activity , but moderated by lower average commission per customer order . cleared customer options and futures contract volumes and stock share volume increased 8 % , 17 % and 12 % , respectively , from the prior year . total darts for cleared and execution-only customers , for the current year , increased 14 % to 647 thousand , compared to 566 thousand during the prior year . darts for cleared customers , i.e . , customers for whom we execute trades , as well as , clear and carry positions , for the current year , increased 14 % to 589 thousand , compared to 515 thousand for the prior year . average commission per dart for cleared customers , for the current year , decreased by 2 % to $ 4.07 , compared to $ 4.16 for the prior year . interest income and interest expense net interest income ( interest income less interest expense ) , for the current year , increased $ 81 million , or 24 % , to $ 425 million , compared to the prior year . the increase in net interest income was driven by higher average customer margin borrowings , higher average customer cash balances which were invested in interest-bearing instruments ( e.g . , u.s. government securities ) , and higher net fees earned from securities lending transactions . net interest income on customer balances , for the current year , increased $ 66 million , compared to the prior year , driven by a $ 5.0 billion increase in average customer cash balances , which were invested in interest-bearing instruments ( e.g . , u.s. government securities ) , and a $ 1.6 billion increase in average customer margin borrowings . in addition , the average fed funds effective rate increased by approximately four basis points to 0.13 % for the current year , compared to the prior year . we earn fees on securities loaned and borrowed to support

customer bad debt customer bad debt expense , in 2014 , decreased $ 64 million , to $ 3 million , compared to 2013 , mainly due to the non-recurrence of customer bad debt recognized in 2013 related to the singapore stock issue discussed below . in october 2013 , a small number of our brokerage customers had taken relatively large positions in four securities listed on the singapore exchange . in early october 2013 , within a very short timeframe , these securities lost over 90 % of their value . the customer accounts were margined and fell into deficits totaling $ 64 million prior to the time we took possession of their securities positions . income tax expense income tax expense , in 2014 , increased $ 14 million , or 42 % , to $ 47 million , compared to 2013 , while income before taxes increased $ 55 million , or 12 % , during the same period . the increase in income tax expense is due to additional amortization of the deferred tax asset arising from the step-up in tax basis of our interests in ibg llc , as a result of the 2013 and 2014 membership interest redemptions from holdings . in addition , in 2013 , we recognized greater tax benefits related to prior years , than in 2014. supplemental information the following tables present historical trading volumes for our business . however , volumes are not the only drivers in our business . trade volumes : ( in 000 's , except % ) replace_table_token_12_th contract and share volumes : ( in 000 's , except % ) total replace_table_token_13_th notes : ( 1 ) futures contract volume includes options on futures 59 market making replace_table_token_14_th brokerage total replace_table_token_15_th brokerage cleared replace_table_token_16_th notes : ( 1 ) futures contract volume includes options on futures 60 brokerage statistics : ( in 000 's , except % and where noted ) replace_table_token_17_th * excludes non-customers . * * the calculation has been revised to exclude components of other income that are not direct revenues from customers . prior period amounts have been recalculated to conform to the current methodology . business segments the following sections discuss the results of our operations by business segment , excluding a discussion of corporate segment income and expense .


 Write a concise suspicious activity report of the following text delimited by triple backquotes. Return your response as a formal report which covers the key points highlighting the location,dates,entity names and account holder information in chronological order of the text.
     ```customer bad debt customer bad debt expense , in 2014 , decreased $ 64 million , to $ 3 million , compared to 2013 , mainly due to the non-recurrence of customer bad debt recognized in 2013 related to the singapore stock issue discussed below . in october 2013 , a small number of our brokerage customers had taken relatively large positions in four securities listed on the singapore exchange . in early october 2013 , within a very short timeframe , these securities lost over 90 % of their value . the customer accounts were margined and fell into deficits totaling $ 64 million prior to the time we took possession of their securities positions . income tax expense income tax expense , in 2014 , increased $ 14 million , or 42 % , to $ 47 million , compared to 2013 , while income before taxes increased $ 55 million , or 12 % , during the same period . the increase in income tax expense is due to additional amortization of the deferred tax asset arising from the step-up in tax basis of our interests in ibg llc , as a result of the 2013 and 2014 membership interest redemptions from holdings . in addition , in 2013 , we recognized greater tax benefits related to prior years , than in 2014. supplemental information the following tables present historical trading volumes for our business . however , volumes are not the only drivers in our business . trade volumes : ( in 000 's , except % ) replace_table_token_12_th contract and share volumes : ( in 000 's , except % ) total replace_table_token_13_th notes : ( 1 ) futures contract volume includes options on futures 59 market making replace_table_token_14_th brokerage total replace_table_token_15_th brokerage cleared replace_table_token_16_th notes : ( 1 ) futures contract volume includes options on futures 60 brokerage statistics : ( in 000 's , except % and where noted ) replace_table_token_17_th * excludes non-customers . * * the calculation has been revised to exclude components of other income that are not direct revenues from customers . prior period amounts have been recalculated to conform to the current methodology . business segments the following sections discuss the results of our operations by business segment , excluding a discussion of corporate segment income and expense .
```    
 Suspicious Activity Report : for examples , we offer prime brokerage services , including capital introduction and securities lending to hedge funds ; and our model portfolio technology and automated share allocation and rebalancing tools are particularly attractive to financial advisors . we provide a host of analytical tools such as the probability lab sm , which allows our customers to analyze option strategies under various market assumptions . the ib investors ' marketplace sm allows wealth advisors to search for money managers and assign them to client accounts based on their investment strategy . ib employeetrack sm is widely used by compliance officers of financial institutions to streamline the process of tracking their employees ' brokerage activities . portfolio builder allows our customers to set up an investment strategy based on research and rankings from top buy-side providers and fundamental data . in addition , ria compliance center provides information to assist advisors with registration and compliance obligations . market making . we conduct our market making business primarily through our th subsidiaries . as one of the largest market makers on many of the world 's leading exchanges , we provide liquidity by offering competitively tight bid/offer spreads over a broad base of over one million tradable , exchange-listed products . as principal , we commit our own capital and derive revenues or incur losses from the difference between the price paid when securities are bought and the price received when those securities are sold . because we provide continuous bid and offer quotations and we are continuously both buying and selling quoted securities , we may have either a long or a short position in a particular product at a given point in time . our entire portfolio is evaluated each second and continuously rebalanced throughout the trading day , thus minimizing the risk of our portfolio at all times . this real-time rebalancing of our portfolio , together with our real-time proprietary risk management system , enables us to curtail risk and to be profitable in both up-market and down-market scenarios . in the past several years our market making business has suffered from competitive pressures and along with the rapid increase of our electronic brokerage business , its significance has diminished . the operating business segments are supported by our corporate segment which provides centralized services and executes our currency diversification strategy . business environment the operating environment for our brokerage business continued to exhibit positive trends in 2015. investor uncertainty accompanied a downdraft in the equity markets in the third quarter of 2015 , and a period of increased volatility led to a contraction of margin borrowings but higher trading volumes . we maintained our position as the largest u.s. electronic broker as measured by number of customer revenue trades , which increased 14 % over the prior year , driving a 12 % increase in commissions and execution fees . new customer account growth continued to gain momentum as total customer accounts increased 18 % to 331 thousand in 2015. institutional customers , such as hedge funds , mutual funds , introducing brokers , proprietary trading groups and financial advisors , comprised approximately 44 % of total accounts and approximately 64 % of total customer equity at the end of 2015. our customer base continues to be geographically diversified , as our customers reside in over 190 countries and over 50 % of new customers came from outside the u.s. average equity per account increased by 1 % , to $ 204 thousand as of december 31 , 2015 . 45 customers continued to take advantage of our low margin lending rates , which are tied to benchmark rates , such as the federal funds rate in the u.s. in 2015 , our customers paid 0.5 % to 1.86 % for their u.s. dollar margin loans with us . after building steadily for a number of years , customer margin loans increased by only 1 % from 2014 , as customers responded to the volatile markets by reducing their leverage . in spite of the modest growth in customer margin loans , electronic brokerage net interest income grew 24 % in 2015 , because average customer credit balances and margin loans for the year were up 18 % and 10 % , respectively . market making segment results increased in 2015 driven by higher market volatility and periods of higher trading activity . the following is a summary of the key profit drivers that affect our business and how they compared to the prior year : global trading volumes . according to data received from exchanges worldwide , volumes in exchange-listed equity-based options increased by approximately 10 % globally and decreased 3 % in the u.s. for the year ended december 31 , 2015 , compared to 2014. during 2015 ( 2014 ) we accounted for approximately 7.8 % ( 8.5 % ) of the exchange-listed equity-based options ( including options on etfs and stock index products ) volume traded worldwide and approximately 11.3 % ( 11.2 % ) of exchange-listed equity-based options volume traded in the u.s. it is important to note that this metric is not directly correlated with our profits . see the tables on pages 59-60 of this annual report on form 10-k for additional details regarding our trade volumes , contract and share volumes and brokerage statistics . volatility . our market making profits are generally correlated with market volatility since we typically maintain an overall long volatility position , which protects us against a severe market dislocation in either direction . based on the chicago board options exchange volatility index ( `` vix® `` ) , the average volatility increased to 16.7 in 2015 , an increase of 18 % from the average of 14.2 in 2014. the ratio of actual to implied volatility is also meaningful to our results . story_separator_special_tag additional consolidation among market centers may adversely affect the value of our smart routing software . a driver of our market making profits is the relationship between actual and implied volatility in the equities markets . the cost of maintaining our conservative risk profile is based on implied volatility , while our profitability , in part , is based on actual volatility . hence , our profitability is increased when actual volatility runs above implied volatility and it is decreased when actual volatility falls below implied volatility . implied volatility tends to lag actual volatility . see `` risk factors `` in part i , item 1a of this annual report on form 10-k for a discussion of other risks that may affect our financial condition and results of operations . 51 results of operations the tables in the period comparisons below provide summaries of our consolidated results of operations . the period-to-period comparisons below of financial results are not necessarily indicative of future results . replace_table_token_10_th 52 the following table sets forth our consolidated results of operations as a percent of our total net revenues for the indicated periods : replace_table_token_11_th year ended december 31 , 2015 ( `` current year `` ) compared to the year ended december 31 , 2014 ( `` prior year `` ) net revenues total net revenues , for the current year , increased $ 146 million , or 14 % , to $ 1,189 million , compared to the prior year . the increase in net revenues was primarily due to higher commissions and execution fees and net interest income . trading volume is an important driver of revenues and costs for both our electronic brokerage and market making segments . during the current year , our futures contract and stock share volumes increased 14 % and 12 % , respectively , while options contract volume remained unchanged , compared to the prior year . trading gains trading gains , for the current year , increased $ 8 million , or 3 % , to $ 269 million , compared to the prior year . as market makers , we provide liquidity by buying from sellers and selling to buyers . during the current year , our market making operations executed 65.9 million trades , an increase of 2 % compared to the number of trades executed in the prior year . market making stock share volume increased 28 % , while options and futures contract volumes decreased 3 % and 4 % , respectively , compared to the prior year . 53 trading gains were favorably impacted by higher volatility levels and periods of higher trading activity . the vix® , which measures perceived u.s. equity market volatility , increased 18 % to an average of 16.7 for the current year , compared to an average of 14.2 for the prior year . the ratio of actual to implied volatility increased to an average of 88 % for the current year , compared to an average of 79 % for the prior year . included in trading gains are net dividends . dividend income and expense arise from holding market making positions over dates on which dividends are paid to shareholders of record . when a stock pays a dividend , its market price is generally adjusted downward to reflect the value paid , which will not be received by those who purchase stock after the ex-dividend date . hence , the apparent gains and losses due to these price changes , reflecting the value of dividends paid to shareholders , must be taken together with the dividends paid and received , respectively , to accurately reflect the results of our market making operations . commissions and execution fees commissions and execution fees , for the current year , increased $ 68 million , or 12 % , to $ 617 million , compared to the prior year , driven by continued customer account growth and increased customer trading activity , but moderated by lower average commission per customer order . cleared customer options and futures contract volumes and stock share volume increased 8 % , 17 % and 12 % , respectively , from the prior year . total darts for cleared and execution-only customers , for the current year , increased 14 % to 647 thousand , compared to 566 thousand during the prior year . darts for cleared customers , i.e . , customers for whom we execute trades , as well as , clear and carry positions , for the current year , increased 14 % to 589 thousand , compared to 515 thousand for the prior year . average commission per dart for cleared customers , for the current year , decreased by 2 % to $ 4.07 , compared to $ 4.16 for the prior year . interest income and interest expense net interest income ( interest income less interest expense ) , for the current year , increased $ 81 million , or 24 % , to $ 425 million , compared to the prior year . the increase in net interest income was driven by higher average customer margin borrowings , higher average customer cash balances which were invested in interest-bearing instruments ( e.g . , u.s. government securities ) , and higher net fees earned from securities lending transactions . net interest income on customer balances , for the current year , increased $ 66 million , compared to the prior year , driven by a $ 5.0 billion increase in average customer cash balances , which were invested in interest-bearing instruments ( e.g . , u.s. government securities ) , and a $ 1.6 billion increase in average customer margin borrowings . in addition , the average fed funds effective rate increased by approximately four basis points to 0.13 % for the current year , compared to the prior year . we earn fees on securities loaned and borrowed to support

