Most Internet users are familiar with ad injectors that insert ads on a Web page. Recent reports have given examples of how in some cases the adware comes preloaded on machines, affecting Google Chrome, Internet Explorer, and Mozilla Firefox browsers on Google searches and on websites. Google in a blog on Tuesday has detailed how it limits or entirely prohibits ad injectors.Additionally, Internet giant has come out with a study conducted with researchers at University of California Berkeley. The study drew conclusions from over 100 million page views of Google sites across various browsers including Google’s Chrome, Mozilla’s Firefox, and Microsoft’s Internet Explorer on various operating systems, globally.

In a blog post titled “Out with unwanted ad injectors,” Google claims that any extension that is hosted in its Chrome Web Store has to comply with the company’s Developer Program Policies, which make sure that these extensions have an “easy-to-understand purpose.” The company notes that it doesn’t ban ad injectors altogether, which means people can still install these.

google_unwanted_ad_injector_blog.jpgIt adds, “We don’t ban injectors altogether-if they want to, people can still choose to install injectors that clearly disclose what they do-but injectors that sneak ads into a user’s browser would certainly violate our policies.”

(Also see: and Other Sites Bundling Superfish-Style Adware: Report)

In addition to this, Google’s DoubleClick Ad Exchange (AdX) Seller Program Guidelines and Google Platforms program policies make sure that no program overlays ad space without prior permission of the site owner.

Google will be releasing a study in May that deals with the ad injector ecosystem in depth. Some of the key findings of the study already revealed include the finding that over 5 percent of people visiting Google sites have at least one ad injector installed (of these, half have at least two injectors installed and nearly one-third have at least four installed); 34 percent of ad injector Chrome extensions were classified as outright malware, and ad injectors were detected on all the operating systems (Mac and Windows) and Web browsers (Chrome, Firefox, IE) included in the test.

The researchers also found 192 deceptive Chrome extensions that were estimated to affect 14 million users. Google says that these have since been disabled, and that it now incorporates the techniques researchers used to catch these extensions to scan all new and updated extensions.