The Moscow-based company's products began blocking some pages with Google's contextual advertising technology, after an erroneous signature was added to its databases. When users visited an affected web resource, a message was displayed stating that the page contained the malicious program Trojan.JS.Redirector.ar.
Kaspersky acknowledged the flaw yesterday. "An incorrect signature was added to the company's antivirus databases on 25 January at 07:00 Moscow time (GMT+3). As a result, Kaspersky Lab products erroneously blocked some legitimate websites containing the link on script http://pagead2.googlesyndication.com/pagead/show_ads.js, which is used in the contextual advertising system Google Adsense," said the anti-malware company in a statement.
The problem would have caused significant concern, especially for users of Internet Explorer 6, which was recently found to be susceptible to a zero-day attack (now patched by Microsoft). It even led to worries that Google itself had been compromised.
One participant on Kaspersky's forums, whose wife used IE 6, said: "It just started about half hour ago.) Sounds like Kasp may have a bug, or, alternately that GoogleSyndication has been penetrated. I sure hope it ain't the latter, cause if it is, gonna be a whole lotta infected pcs."
The problem occurred just hours after the company also added the entire bit.ly URL shortening service to its signature list, meaning that any link shortened and sent via bit.ly would be shown as malicious. This will be particularly embarassing for Kaspersky, given its public relations activity over the Krab Krawler research project into bit.ly and its owners, who also own the Twitter micro-blogging service, late last year.
However, Kaspersky moved quickly to fix both of the issues. "The problem was quickly resolved and by 19:00 Moscow time the company's products had stopped generating alerts for legitimate Internet pages," Kaspersky said.
This is not the first time that Google has suffered at the hands of anti-malware companies. Symantec's Norton Internet Security was also found to be blocking AdSense-based sites in 2006.