Scammers have quickly piggybacked onto news of a faulty McAfee antivirus update that crippled thousands of computers, according  to security researchers.

On Wednesday, McAfee released a flawed signature update that wrongly labelled a crucial system file in Windows XP Service Pack 3 (SP3) as malware. After the software quarantined the 'svchost.exe' file, thousands of PCs, most of them in businesses, crashed and rebooted repeatedly.

Firms are still dealing with the aftermath, with some companies forced to manually reconfigure hundreds or even thousands of systems.

But it didn't take long for scammers to get in on the act. Using their now-traditional technique of poisoning results at majorsearch engines like Google and Bing, 'scareware' makers have pushed links touting fake antivirus software to at or near the top of the results lists, said Graham Closely, senior technology consultant with Sophos.

The links appear when users type search terms such as 'McAfee update' and 'McAfee 5958', the latter a reference to the faulty update's designation, added Panda Security in a post to its company blog.

"If you click on a dangerous link like this, then you risk the chance of your computer being hit by a fake antivirus attack, which may attempt to con you out of your credit card details or trick you into install[ing] malicious code onto your computer," said Cluley in a post to his blog .

McAfee owned up to the problem - Barry McPherson, executive vice president of support, said 'No excuses on Wednesday - and the company has posted guides to help businesses and consumers restore incapacitated PCs. On Wednesday afternoon, McAfee issued a replacement update for the faulty signature file.

That did little to soothe some frustrated users. "Today has been a nightmare. Maybe time to look at a new virus solutions once the licence expires," said a user identified as 'alomas' on a McAfee corporate support forum thread that has nearly 150 messages. "Could not handle another day like this and confidence in McAfee at an all time low."

Fake security software is a very lucrative and thus popular part of the cybercrime ecology. According to a 2008 report, crooks can make as much as $5 million annually in the practice. McAfee rival Symantec, meanwhile, recently reported that the second-most-downloaded piece of malware during 2009 was the "FakeAV" Trojan horse, which displays false alerts and lowers security settings on compromised PCs. The phony alerts try to dupe users into heading to a site where they can download the sham software.

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