A study by Google says that fake anti-virus software carrying malicious code is a growing threat.
The search engine outfit says that more and more scammers are using bogus warnings about infected computers to trick gullible punters into installing fake software which actually does even more damage.
The company reckons that AV scams now account for as much as 15 per cent of all the malicious code out there.
It also said that more than half of the malicious content was delivered via adverts by sophisticated criminals who are using black hat search engine optimisation techniques in order to boost their search rankings to the top spot on Google.
There are currently more than 11,000 web domains pumping out fake AV software according to the BBC.