Posted by Kurt Thomas, Spam &amp; Abuse Research In March, we outlined the problems with unwanted ad injectors, a common symptom of unwanted software. Ad injectors are programs that insert new ads, or replace existing ones, into the pages you visit while browsing the web. We’ve received more than 100,000 user complaints about them in Chrome since the beginning of 2015—more than any other issue. Unwanted ad injectors are not only annoying, they can pose serious security risks to users as well. Today, we’re releasing the results of a study performed with the University of California, Berkeley and Santa Barbara that examines the ad injector ecosystem, in-depth, for the first time. We’ve summarized our key findings below, as well as Google’s broader efforts to protect users from unwanted software. The full report, which you can read here, will be presented later this month at the IEEE Symposium on Security &amp; Privacy. Ad injectors’ businesses are built on a tangled web of different players in the online advertising economy. This complexity has made it difficult for the industry to understand this issue and help fix it. We hope our findings raise broad awareness of this problem and enable the online advertising industry to work together and tackle it. How big is the problem? This is what users might see if their browsers were infected with ad injectors. None of the ads displayed appear without an ad injector installed. To pursue this research, we custom-built an ad injection “detector” for Google sites. This tool helped us identify tens of millions of instances of ad injection “in the wild” over the course of several months in 2014, the duration of our study. More detail is below, but the main point is clear: deceptive ad injection is a significant problem on the web today. We found 5.5%!o(MISSING)f unique IPs—millions of users—accessing Google sites that included some form of injected ads. How ad injectors work The ad injection ecosystem comprises a tangled web of different players. Here is a quick snapshot. Software: It all starts with software that infects your browser. We discovered more than 50,000 browser extensions and more than 34,000 software applications that took control of users’ browsers and injected ads. Upwards of 30%!o(MISSING)f these packages were outright malicious and simultaneously stole account credentials, hijacked search queries, and reported a user’s activity to third parties for tracking. In total, we found 5.1%!o(MISSING)f page views on Windows and 3.4%!o(MISSING)f page views on Mac that showed tell-tale signs of ad injection software. Distribution: Next, this software is distributed by a network of affiliates that work to drive as many installs as possible via tactics like: marketing, bundling applications with popular downloads, outright malware distribution, and large social advertising campaigns. Affiliates are paid a commision whenever a user clicks on an injected ad. We found about 1,000 of these businesses, including Crossrider, Shopper Pro, and Netcrawl, that use at least one of these tactics. Injection Libraries: Ad injectors source their ads from about 25 businesses that provide ‘injection libraries’. Superfish and Jollywallet are by far the most popular of these, appearing in 3.9%!a(MISSING)nd 2.4%!o(MISSING)f Google views, respectively. These companies manage advertising relationships with a handful of ad networks and shopping programs and decide which ads to display to users. Whenever a user clicks on an ad or purchases a product, these companies make a profit, a fraction of which they share with affiliates. Ads: The ad injection ecosystem profits from more than 3,000 victimized advertisers—including major retailers like Sears, Walmart, Target, Ebay—who unwittingly pay for traffic to their sites. Because advertisers are generally only able to measure the final click that drives traffic to their sites, they’re often unaware of many preceding twists and turns, and don’t know they are receiving traffic via unwanted software and malware. Ads originate from ad networks that translate unwanted software installations into profit: 77%!o(MISSING)f all injected ads go through one of three ad networks—dealtime.com, pricegrabber.com, and bizrate.com. Publishers, meanwhile, aren’t being compensated for these ads. Examples of injected ads ‘in the wild’ How Google fights deceptive ad injectors  We pursued this research to raise awareness about the ad injection economy so that the broader ads ecosystem can better understand this complex issue and work together to tackle it. Based on our findings, we took the following actions: Keeping the Chrome Web Store clean: We removed 192 deceptive Chrome extensions that affected 14 million users with ad injection from the Chrome Web Store. These extensions violated Web Store policies that extensions have a narrow and easy-to-understand purpose. We’ve also deployed new safeguards in the Chrome Web Store to help protect users from deceptive ad injection extensions. Protecting Chrome users: We improved protections in Chrome to flag unwanted software and display familiar red warnings when users are about to download deceptive software. These same protections are broadly available via the Safe Browsing API. We also provide a tool for users already affected by ad injectors and other unwanted software to clean up their Chrome browser. Informing advertisers: We reached out to the advertisers affected by ad injection to alert each of the deceptive practices and ad networks involved. This reflects a broader set of Google Platforms program policies and the DoubleClick Ad Exchange (AdX) Seller Program Guidelines that prohibit programs overlaying ad space on a given site without permission of the site owner. Most recently, we updated our AdWords policies to make it more difficult for advertisers to promote unwanted software on AdWords. It&#39;s still early, but we&#39;ve already seen encouraging results since making the change: the number of &#39;Safe Browsing&#39; warnings that users receive in Chrome after clicking AdWords ads has dropped by more than 95%! (MISSING)This suggests it&#39;s become much more difficult for users to download unwanted software, and for bad advertisers to promote it. Our blog post from March outlines various policies—for the Chrome Web Store, AdWords, Google Platforms program, and the DoubleClick Ad Exchange (AdX)—that combat unwanted ad injectors, across products. We’re also constantly improving our Safe Browsing technology, which protects more than one billion Chrome, Safari, and Firefox users across the web from phishing, malware, and unwanted software. Today, Safe Browsing shows people more than 5 million warnings per day for all sorts of malicious sites and unwanted software, and discovers more than 50,000 malware sites and more than 90,000 phishing sites every month. Considering the tangle of different businesses involved—knowingly, or unknowingly—in the ad injector ecosystem, progress will only be made if we raise our standards, together. We strongly encourage all members of the ads ecosystem to review their policies and practices so we can make real improvement on this issue. 