every person who ta kes a survey is a potential future customer , and we seek to capitalize on that opportunity through end of survey marketing designed to engage further with respondents and encourage them to create accounts and become new users . we invest in new features and improvements to our product functionality as well as targeted marketing campaigns to drive conversion of unpaid users to paid users . as a result , we have a predictable , high-visibility revenue model where we generate more than 90 % our revenue from sales o f subscriptions to our products . we have a broad and diverse customer base and no customer represented more than 1 % of our revenue in any of the periods presented . we supplement our self-serve channel with a targeted sales effort to upsell organizations to surveymonkey enterprise , to expand deployments of surveymonkey enterprise within organizations and to cross-sell purpose-built solutions within organizations . we believe our existing user base represents a significant opportunity to expand our business and increase our revenue . we have 646,727 paying users in more than 345,000 organizational domains and believe the individual paying users within organizational domains represent an opportunity to significantly increase conversion from individual subscriptions to our enterprise offerings . key business metric we review a number of operating and financial metrics , including the following key metric to evaluate our business , measure our performance , identify trends affecting our business , formulate our business plan and make strategic decisions . replace_table_token_6_th paying users we define a paying user as an individual customer of our survey platform or form-based application , a seat within a surveymonkey enterprise deployment or a subscription to one of our purpose-built solutions , in each case as of the end of a period . one person would count as multiple paying users if the person had more than one paid license at the end of the period . for example , if an individual paying user also had a designated seat in a surveymonkey enterprise deployment , we would count that person as two paying users . paying users is an indicator of the scale of our business and an important factor in our ability to increase our revenue . non-gaap financial measures we believe that , in addition to our results determined in accordance with gaap , core revenue , average revenue per paying user , free cash flow and adjusted ebitda , all of which are non-gaap financial measures , are useful in evaluating our business , results of operations and financial condition . replace_table_token_7_th core revenue we define core revenue as revenue from our survey platform , form-based application and purpose-built solutions , excluding the non-self-serve portion of surveymonkey audience , which we generally ceased offering at the end of the second quarter of 2017. we consider core revenue to be an important measure because it excludes revenue from an offering that we generally no longer provide , and so provides a better understanding of our current 45 business and provides comparability of our results of operations over ti me . core revenue has limitations as an analytical tool , and it should not be considered in isolation or as a substitute for analysis of other gaap financial measures , such as revenue . some of the limitations of core revenue are that it does not reflect all of our revenue in the periods presented and that our results of operations for the periods presented reflect expenses that we incurred to generate revenue that is excluded fr om core revenue . the following is a reconciliation of core revenue to the most comparable gaap measure , revenue : replace_table_token_8_th average revenue per paying user we define average revenue per paying user , or arpu , as core revenue divided by the average number of paying users during the period . for interim periods , we use annualized core revenue which is calculated by dividing the core revenue for the period by the number of days in that period and multiplying this value by 365 days . we calculate the average number of paying users by adding the number of paying users as of the end of the prior period to the number of paying users as of the end of the current period , and then dividing by two . we consider arpu to be an important measure because it helps illustrate underlying trends in our business by showing investors the changes in per-user revenue , which is a reflection of our ability to successfully upsell or cross-sell our products and purpose-built solutions . arpu has limitations as an analytic tool , and it should not be considered in isolation or as a substitute for analysis of other gaap financial measures . some of the limitations of arpu are that it is a calculation that does not reflect revenue from the non-self-serve portion of our surveymonkey audience solution in any of the periods presented , and also does not reflect expenses that we incurred to generate revenue that is excluded from core revenue . free cash flow we define free cash flow as gaap net cash provided by operating activities less purchases of property and equipment , net of tenant improvement reimbursements , and capitalized internal-use software . we consider free cash flow to be an important measure because it measures our liquidity after deducting capital expenditures for purchases of property and equipment and capitalized software development costs , which we believe provides a more accurate view of our cash generation and cash available to grow our business . for the years ended december 31 , 2018 , 2017 and 2016 , our free cash flow included cash payments for interest on our long-term debt of $ 20.5 million , $ 19.9 million and $ 19.8 million , respectively . story_separator_special_tag in addition , we incurred $ 3.2 million of transaction fees during the year ended december 31 , 2017 related to our 2017 credit facility as compared to $ 0.9 million incurred during the year ended december 31 , 2018 , related to our 2018 credit facility . restructuring year ended december 31 , ( dollars in thousands ) 2018 2017 change % change restructuring $ 3,525 $ 1,785 $ 1,740 97 % restructuring expenses increased for the year ended december 31 , 2018 compared to the prior year , primarily due to the $ 2.8 million write-off of leasehold improvements related to our november 2017 restructuring plan . 52 interest expense year ended december 31 , ( dollars in thousands ) 2018 2017 change % change interest expense $ 27,801 $ 26,865 $ 936 3 % interest expense increased for the year ended december 31 , 2018 compared to the prior year , primarily due to higher average interest rates . we expect future interest expense to decrease resulting from the repayment of a portion of our outstanding indebtedness under our credit facilities and our adoption of the new leasing standard , asc 842. for additional information regarding our credit facilities and financing obligations , see notes 8 and 9 , respectively , of the notes to consolidated financial statements included elsewhere in this annual report on form 10-k. other non-operating income , net year ended december 31 , ( dollars in thousands ) 2018 2017 change % change other non-operating income ( expense ) , net $ ( 298 ) $ 7,610 $ ( 7,908 ) ( 104 ) % other non-operating income , net decreased for the year ended december 31 , 2018 compared to the prior year , primarily due to a decrease of $ 5.6 million gain on our sale of a private company investment , an increase in foreign currency losses of $ 1.5 million , an increase in loss on debt refinancing of $ 0.8 million , partially offset by an increase in interest income of $ 1.1 million resulting from higher average cash balances . provision for income taxes replace_table_token_16_th the provision for income taxes increased for the year ended december 31 , 2018 compared to the prior year , primarily due to certain provisions in the tax act , including a decrease in the u.s. statutory tax rate from 35 % to 21 % and changes to our valuation allowance . comparison of the year ended december 31 , 2017 and 2016 revenue and cost of revenue replace_table_token_17_th revenue increased for the year ended december 31 , 2017 compared to the prior year primarily due to a 5 % increase the number of paying users from 574,872 in 2016 to 606,077 in 2017. the increase in revenue was also due in part to a 4 % increase in arpu from $ 349 in 2016 to $ 362 in 2017 , which was largely driven by a change to our individual user plans in 2017 that offered paying users new plans with more functionality and required our users to renew their subscriptions at higher price points . the increase in revenue was partially offset by a $ 10.5 million decrease in revenue relating to us having ceased offering our non-self-serve version of our surveymonkey audience solution at the end of the second quarter of 2017. during the year ended december 31 , 2017 , we 53 generated over 75 % of our revenue from individuals and organizations that were customers in 2016 , with the remainder of our revenue coming from new customers . cost of revenue decreased for the year ended december 31 , 2017 compared to the prior year , primarily due to a $ 2.5 million decrease in amortization of developed technology due to the de-recognition of acquired intangibles , a $ 2.0 million decrease in external sample costs as we generally ceased offering our non-self-serve version of our surveymonkey audience solution at the end of the second quarter of 2017 , a $ 2.9 million decrease in personnel costs due to a decrease in headcount and a $ 1.2 million decrease in external services . these decreases were partially offset by increases of $ 2.2 million in the amortization of capitalized software , $ 0.7 million in facilities costs and $ 0.6 million in payment processing fees due to increased sales . as a result of the increase in our revenue and the decrease in our cost of revenue , our gross margin increased for the year ended december 31 , 2017 as compared to the prior year . research and development year ended december 31 , ( dollars in thousands ) 2017 2016 change % change research and development $ 53,660 $ 37,985 $ 15,675 41 % research and development expenses increased for the year ended december 31 , 2017 compared to the prior year primarily due to an increase of $ 9.7 million in personnel costs due to headcount growth , a $ 2.6 million decrease in the software development costs that qualified for capitalization and a $ 3.7 million increase in facilities costs related to the relocation of our headquarters . these increases were partially offset by acquisition-related deferred compensation becoming fully amortized in 2016. sales and marketing year ended december 31 , ( dollars in thousands ) 2017 2016 change % change sales and marketing $ 73,511 $ 73,970 $ ( 459 ) ( 1 ) % sales and marketing expenses decreased for the year ended december 31 , 2017 compared to the prior year , primarily due to decreases of $ 5.0 million in acquisition-related expenses due to deferred compensation related to past acquisitions becoming fully amortized in 2016 , $ 1.8 million in intangible asset amortization due to certain acquired intangible assets becoming fully amortized in 2016 , $ 1.0 million in commissions expense related to our non-self-serve version of surveymonkey audience solution , which we generally ceased offering at the end

cash flows from operating activities our largest source of operating cash is cash collections from our customers for subscriptions to our products . our primary uses of cash in operating activities are for employee-related expenditures , marketing expenses and third-party hosting costs . historically , we have generated positive cash flows from operating activities . net cash provided by operating activities is impacted by our net loss adjusted for certain non-cash items , including depreciation and amortization expenses , stock-based compensation , the derecognition of goodwill and intangible assets in 2016 , deferred income taxes , as well as the effect of changes in operating assets and liabilities . during the year ended december 31 , 2018 , cash provided by operating activities was $ 45.4 million , primarily due to our net loss of $ 154.7 million , adjusted for non-cash charges of $ 183.9 million and net cash inflows of $ 16.2 million provided by changes in our operating assets and liabilities . non-cash charges primarily consisted of depreciation and amortization of property and equipment , capitalized internal-use software and intangible assets , and stock-based compensation . the primary drivers of the changes in operating assets and liabilities related to cash provided by a $ 16.4 million increase in deferred revenue , a $ 5.2 million increase in accrued compensation and a $ 3.6 million increase in accounts payable and accrued liabilities , partially offset by cash used for prepaid expenses and other assets of $ 5.6 million , as well as an increase in accounts receivable of $ 2.0 million and a decrease of $ 1.4 million in accrued interest on financing lease obligation . during the year ended december 31 , 2017 , cash provided by operating activities was $ 45.0 million , primarily due to our net loss of $ 24.0 million , adjusted for non-cash charges of $ 54.0 million and net cash inflows of $ 15.0 million provided by changes in our operating assets and liabilities .


 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.
     ```cash flows from operating activities our largest source of operating cash is cash collections from our customers for subscriptions to our products . our primary uses of cash in operating activities are for employee-related expenditures , marketing expenses and third-party hosting costs . historically , we have generated positive cash flows from operating activities . net cash provided by operating activities is impacted by our net loss adjusted for certain non-cash items , including depreciation and amortization expenses , stock-based compensation , the derecognition of goodwill and intangible assets in 2016 , deferred income taxes , as well as the effect of changes in operating assets and liabilities . during the year ended december 31 , 2018 , cash provided by operating activities was $ 45.4 million , primarily due to our net loss of $ 154.7 million , adjusted for non-cash charges of $ 183.9 million and net cash inflows of $ 16.2 million provided by changes in our operating assets and liabilities . non-cash charges primarily consisted of depreciation and amortization of property and equipment , capitalized internal-use software and intangible assets , and stock-based compensation . the primary drivers of the changes in operating assets and liabilities related to cash provided by a $ 16.4 million increase in deferred revenue , a $ 5.2 million increase in accrued compensation and a $ 3.6 million increase in accounts payable and accrued liabilities , partially offset by cash used for prepaid expenses and other assets of $ 5.6 million , as well as an increase in accounts receivable of $ 2.0 million and a decrease of $ 1.4 million in accrued interest on financing lease obligation . during the year ended december 31 , 2017 , cash provided by operating activities was $ 45.0 million , primarily due to our net loss of $ 24.0 million , adjusted for non-cash charges of $ 54.0 million and net cash inflows of $ 15.0 million provided by changes in our operating assets and liabilities .
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 Suspicious Activity Report : every person who ta kes a survey is a potential future customer , and we seek to capitalize on that opportunity through end of survey marketing designed to engage further with respondents and encourage them to create accounts and become new users . we invest in new features and improvements to our product functionality as well as targeted marketing campaigns to drive conversion of unpaid users to paid users . as a result , we have a predictable , high-visibility revenue model where we generate more than 90 % our revenue from sales o f subscriptions to our products . we have a broad and diverse customer base and no customer represented more than 1 % of our revenue in any of the periods presented . we supplement our self-serve channel with a targeted sales effort to upsell organizations to surveymonkey enterprise , to expand deployments of surveymonkey enterprise within organizations and to cross-sell purpose-built solutions within organizations . we believe our existing user base represents a significant opportunity to expand our business and increase our revenue . we have 646,727 paying users in more than 345,000 organizational domains and believe the individual paying users within organizational domains represent an opportunity to significantly increase conversion from individual subscriptions to our enterprise offerings . key business metric we review a number of operating and financial metrics , including the following key metric to evaluate our business , measure our performance , identify trends affecting our business , formulate our business plan and make strategic decisions . replace_table_token_6_th paying users we define a paying user as an individual customer of our survey platform or form-based application , a seat within a surveymonkey enterprise deployment or a subscription to one of our purpose-built solutions , in each case as of the end of a period . one person would count as multiple paying users if the person had more than one paid license at the end of the period . for example , if an individual paying user also had a designated seat in a surveymonkey enterprise deployment , we would count that person as two paying users . paying users is an indicator of the scale of our business and an important factor in our ability to increase our revenue . non-gaap financial measures we believe that , in addition to our results determined in accordance with gaap , core revenue , average revenue per paying user , free cash flow and adjusted ebitda , all of which are non-gaap financial measures , are useful in evaluating our business , results of operations and financial condition . replace_table_token_7_th core revenue we define core revenue as revenue from our survey platform , form-based application and purpose-built solutions , excluding the non-self-serve portion of surveymonkey audience , which we generally ceased offering at the end of the second quarter of 2017. we consider core revenue to be an important measure because it excludes revenue from an offering that we generally no longer provide , and so provides a better understanding of our current 45 business and provides comparability of our results of operations over ti me . core revenue has limitations as an analytical tool , and it should not be considered in isolation or as a substitute for analysis of other gaap financial measures , such as revenue . some of the limitations of core revenue are that it does not reflect all of our revenue in the periods presented and that our results of operations for the periods presented reflect expenses that we incurred to generate revenue that is excluded fr om core revenue . the following is a reconciliation of core revenue to the most comparable gaap measure , revenue : replace_table_token_8_th average revenue per paying user we define average revenue per paying user , or arpu , as core revenue divided by the average number of paying users during the period . for interim periods , we use annualized core revenue which is calculated by dividing the core revenue for the period by the number of days in that period and multiplying this value by 365 days . we calculate the average number of paying users by adding the number of paying users as of the end of the prior period to the number of paying users as of the end of the current period , and then dividing by two . we consider arpu to be an important measure because it helps illustrate underlying trends in our business by showing investors the changes in per-user revenue , which is a reflection of our ability to successfully upsell or cross-sell our products and purpose-built solutions . arpu has limitations as an analytic tool , and it should not be considered in isolation or as a substitute for analysis of other gaap financial measures . some of the limitations of arpu are that it is a calculation that does not reflect revenue from the non-self-serve portion of our surveymonkey audience solution in any of the periods presented , and also does not reflect expenses that we incurred to generate revenue that is excluded from core revenue . free cash flow we define free cash flow as gaap net cash provided by operating activities less purchases of property and equipment , net of tenant improvement reimbursements , and capitalized internal-use software . we consider free cash flow to be an important measure because it measures our liquidity after deducting capital expenditures for purchases of property and equipment and capitalized software development costs , which we believe provides a more accurate view of our cash generation and cash available to grow our business . for the years ended december 31 , 2018 , 2017 and 2016 , our free cash flow included cash payments for interest on our long-term debt of $ 20.5 million , $ 19.9 million and $ 19.8 million , respectively . story_separator_special_tag in addition , we incurred $ 3.2 million of transaction fees during the year ended december 31 , 2017 related to our 2017 credit facility as compared to $ 0.9 million incurred during the year ended december 31 , 2018 , related to our 2018 credit facility . restructuring year ended december 31 , ( dollars in thousands ) 2018 2017 change % change restructuring $ 3,525 $ 1,785 $ 1,740 97 % restructuring expenses increased for the year ended december 31 , 2018 compared to the prior year , primarily due to the $ 2.8 million write-off of leasehold improvements related to our november 2017 restructuring plan . 52 interest expense year ended december 31 , ( dollars in thousands ) 2018 2017 change % change interest expense $ 27,801 $ 26,865 $ 936 3 % interest expense increased for the year ended december 31 , 2018 compared to the prior year , primarily due to higher average interest rates . we expect future interest expense to decrease resulting from the repayment of a portion of our outstanding indebtedness under our credit facilities and our adoption of the new leasing standard , asc 842. for additional information regarding our credit facilities and financing obligations , see notes 8 and 9 , respectively , of the notes to consolidated financial statements included elsewhere in this annual report on form 10-k. other non-operating income , net year ended december 31 , ( dollars in thousands ) 2018 2017 change % change other non-operating income ( expense ) , net $ ( 298 ) $ 7,610 $ ( 7,908 ) ( 104 ) % other non-operating income , net decreased for the year ended december 31 , 2018 compared to the prior year , primarily due to a decrease of $ 5.6 million gain on our sale of a private company investment , an increase in foreign currency losses of $ 1.5 million , an increase in loss on debt refinancing of $ 0.8 million , partially offset by an increase in interest income of $ 1.1 million resulting from higher average cash balances . provision for income taxes replace_table_token_16_th the provision for income taxes increased for the year ended december 31 , 2018 compared to the prior year , primarily due to certain provisions in the tax act , including a decrease in the u.s. statutory tax rate from 35 % to 21 % and changes to our valuation allowance . comparison of the year ended december 31 , 2017 and 2016 revenue and cost of revenue replace_table_token_17_th revenue increased for the year ended december 31 , 2017 compared to the prior year primarily due to a 5 % increase the number of paying users from 574,872 in 2016 to 606,077 in 2017. the increase in revenue was also due in part to a 4 % increase in arpu from $ 349 in 2016 to $ 362 in 2017 , which was largely driven by a change to our individual user plans in 2017 that offered paying users new plans with more functionality and required our users to renew their subscriptions at higher price points . the increase in revenue was partially offset by a $ 10.5 million decrease in revenue relating to us having ceased offering our non-self-serve version of our surveymonkey audience solution at the end of the second quarter of 2017. during the year ended december 31 , 2017 , we 53 generated over 75 % of our revenue from individuals and organizations that were customers in 2016 , with the remainder of our revenue coming from new customers . cost of revenue decreased for the year ended december 31 , 2017 compared to the prior year , primarily due to a $ 2.5 million decrease in amortization of developed technology due to the de-recognition of acquired intangibles , a $ 2.0 million decrease in external sample costs as we generally ceased offering our non-self-serve version of our surveymonkey audience solution at the end of the second quarter of 2017 , a $ 2.9 million decrease in personnel costs due to a decrease in headcount and a $ 1.2 million decrease in external services . these decreases were partially offset by increases of $ 2.2 million in the amortization of capitalized software , $ 0.7 million in facilities costs and $ 0.6 million in payment processing fees due to increased sales . as a result of the increase in our revenue and the decrease in our cost of revenue , our gross margin increased for the year ended december 31 , 2017 as compared to the prior year . research and development year ended december 31 , ( dollars in thousands ) 2017 2016 change % change research and development $ 53,660 $ 37,985 $ 15,675 41 % research and development expenses increased for the year ended december 31 , 2017 compared to the prior year primarily due to an increase of $ 9.7 million in personnel costs due to headcount growth , a $ 2.6 million decrease in the software development costs that qualified for capitalization and a $ 3.7 million increase in facilities costs related to the relocation of our headquarters . these increases were partially offset by acquisition-related deferred compensation becoming fully amortized in 2016. sales and marketing year ended december 31 , ( dollars in thousands ) 2017 2016 change % change sales and marketing $ 73,511 $ 73,970 $ ( 459 ) ( 1 ) % sales and marketing expenses decreased for the year ended december 31 , 2017 compared to the prior year , primarily due to decreases of $ 5.0 million in acquisition-related expenses due to deferred compensation related to past acquisitions becoming fully amortized in 2016 , $ 1.8 million in intangible asset amortization due to certain acquired intangible assets becoming fully amortized in 2016 , $ 1.0 million in commissions expense related to our non-self-serve version of surveymonkey audience solution , which we generally ceased offering at the end

