In December 2008 the company raised $4.5 million in Series B funding and a further $5 million in April 2010. In December 2010 Tumblr raised $30 million in Series D funding. The company had an $800 million valuation in August 2011. In September 2011 the company raised $85 million in a round of funding led by Greylock Partners and Insight Venture Partners. In an interview with Nicole Lapin of "Bloomberg West" on September 7, 2012, David Karp said the site was monetized by advertising. Their first advertising launch started in May 2012 after 16 experimental campaigns. Tumblr made $13 million in revenue in 2012 and hoped to make $100 million in 2013. Tumblr reportedly spent $25 million to fund operations in 2012. In 2013, Tumblr began allowing companies to pay to promote their own posts to a larger audience. Tumblr Head of Sales, Lee Brown, has quoted the average ad purchase on Tumblr to be nearly six figures. Tumblr also allows premium theme templates to be sold for use by blogs. In July 2016, advertisements were implemented by default across all blogs. Users may opt-out, and the service stated that a revenue sharing program would be implemented at a later date. Tumblr has received criticism for copyright violations by participating bloggers; however, Tumblr accepts Digital Millennium Copyright Act (DMCA) take-down notices. Tumblr's visual appeal has made it ideal for photoblogs that often include copyrighted works from others that are re-published without payment. Tumblr users can post unoriginal content by "Reblogging", a feature on Tumblr that allows users to re-post content taken from another blog onto their own blog with attribution. Tumblr has been forced to manage spam and security problems. For example, a chain letter scam in May 2011 affected 130,000 users. On December 3, 2012, Tumblr was attacked by a cross-site scripting worm deployed by the Internet troll group Gay Nigger Association of America. The message urged users to harm themselves and criticized blogging in general. In 2015, Tumblr faced criticism by users for changes to its reblog mechanisms. In July 2015, the system was modified so that users cannot remove or edit individual comments by other users when reblogging a post; existing comments can only be removed all at once. Tumblr staff argued that the change was intended to combat "misattribution", though this move was met by criticism from ‘ask blogs’ and ‘RP blogs’, which often shortened long chains of reblogs between users to improve readability. In September 2015, Tumblr changed how threads of comments on reblogged posts are displayed; rather than a nested view with indentations for each post, all reblogs are now shown in a flat view, and user avatars were also added.