Over five percent of browser visits to Google-owned websites, including Google Search, are altered by computer programs that inject ads into pages. One called Superfish is responsible for a majority of those ad injections.
The findings are the result of a study by Google and researchers from the University of California at Berkeley and Santa Barbara, which analysed over 102 million page views to Google sites between June and September last year.
Google added code to its websites that detected and reported back when ads were injected into pages by programs or browser extensions. This revealed that locally-installed ad injectors interfered with 5,339,913 page views (5.2 percent of the total), impacting tens of millions of users around the world - or 5.5 percent of unique daily IP addresses that accessed Google's sites.
Further analysis of the data helped researchers to identify 50,870 Chrome extensions and 34,407 programs that injected ads. Thirty-eight percent of extensions and 17 percent of programs were catalogued as malware, the rest being potentially unwanted adware-type applications.
Most ad injectors bundle one or more libraries that display ads or perform other tasks. Of those libraries, one called Superfish and one called Jollywallet were the most frequently encountered ones. Superfish injects alternative shopping suggestions in the form of ads based on image similarity searches, while Jollywallet overwrites affiliate parameters in URLs on shopping sites to earn referral commissions without actually driving traffic to the sold product.
Superfish got some attention back in February because it opened a serious security hole on computers, including on some Lenovo consumer laptops that came pre-loaded with it. Lenovo released a clean-up tool and also worked with Microsoft and other security vendors to remove the program from computers.
The researchers behind Google's study found that 49,127 (96 percent) of browser extensions and 33,486 (97 percent) of software programs of the identified ad injectors contacted superfish.com. However, 50 percent of extensions used at least two ad injection libraries and 80 percent of programs used at least four.
Google removed 192 deceptive ad injecting extensions from the Chrome Web Store. However, only 10 percent of such extensions have ever been present in the store, according to the researchers. Most of them have been installed by other programs directly in users' browsers.
To prevent such side-loading, since May last year the Chrome browser blocks the installation of extensions that are not hosted in the Chrome Web Store. Google also provides a removal tool for potentially unwanted programs, including ad injectors, that modify the browser.