Fake antivirus software accounts for as much as 15% of all malicious software scams, Google has claimed.

The search engine giant warned that fake antivirus software presents a growing threat to computer users after an investigation into some 240million web pages over a 13 month period.

The study, which was presented at the Usenix Workshop on Large-Scale Exploits and Emergent Threats in California, analysed websites between January 2009 and February 2010, finding more than 11,000 web domains involved in its distribution of fake antivirus software.

Fake antivirus software scams usually attempt to trick a user into believing that their PC has become infected with a virus or some other form of malware, with a pop-up message encouraging users to download a software package to remedy the problem. The software is then downloaded by an unsuspecting user, which then installs malicious programs onto their PC.

The scams are often distributed when a user visits an infected website, although many well respected websites, including the New York Times, The Daily Telegraph and The Daily Mail, have been caught up in fake antivirus scams after their ad system was hacked.

“Surprisingly, many users fall victim to these attacks and pay to register the fake [anti-virus software],” the study said.

“To add insult to injury, fake anti-viruses often are bundled with other malware, which remains on a victim’s computer regardless of whether a payment is made.”

More than half of the fake software – which predominantly targets Windows machines – was delivered via adverts, Google added.

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