You enter a search term on Google and hit the search button. Up pops a warning message that reads: "Your computer appears to be infected. It appears that your computer is infected with software that intercepts your connection to Google and other sites. Learn how to fix this."

Graham Cluley, senior technology consultant at Sophos Security, said the first time he heard about this he suspected it was one of those clever, fake anti-virus come-ons.

It's not. After doing some checking, Cluley said he learned Google is trying to give consumers a heads-up when it detects their computers aren't fully under their control.

Diverting Google traffic

Damian Menscher, a security engineer at Google, has posted details on his blog, explaining how he discovered that infected computers were sending search traffic through proxies to the search engine.

The intention is purely profit-driven. They hackers that have infected your computer want to modify your search results to highlight money-making pay-per-click sites instead of the sites Google would normally serve up.

In all, Google estimates that a couple of million Windows PCs may be affected around the world by this particular strain of malware. Google says it has already been able to warn hundreds of thousands of computer users their devices are infected.

“Fortunately, although Google does not scan your hard drive when you search for things via, it can detect the unique traffic signature from visiting infected PCs and make a pretty informed guess about your computer's health in regard to this malware strain,” Cluley said in his blog.

Providing security function

Cluley says Google wants the warning message to encourage users to update their anti-virus software, scan their computers and become more conscious of security issues.

“I think what Google is doing should be applauded - anything which warns computer users about genuine malware threats has to be a good thing,” Cluley said.

There is a danger, however, that scammers will quickly mimic the Google warning and offer a cure, which of course, will be more malware. Google, meanwhile, urges consumers to conduct searches for security software for their computers.

In the video below, Cluley notes that, in itself, can be rather dangerous.