A US citizen has been accused of bombarding innocent computer users with pop-up adverts promoting pornography and Viagra in a bid to sell bogus security software.

According to reports, Ron Cooke, owner of Messenger Solutions, has been accused of violating Washington's Computer Spyware Act and Consumer Protection Act when marketing his WinAntiVirus Pro 2007, System Doctor, Messenger Blocker and WinAntiSpyware products.

A lawsuit filed in Seattle's King County Superior Court alleges that internet users were coerced into purchasing the software after pop-up adverts were sent via the Windows Messenger Net Send system.

Consumers who downloaded the software are said to have unwittingly bombarded other computer users with pop-up messages advertising pornography and drugs every two seconds.

"Our suit alleges that it was not enough for Ron Cooke to manipulate consumers into buying his software," said Washington Attorney General Rob McKenna. "His program also maliciously turns victims' computers into spamming machines."

Graham Cluley, senior technology consultant at Sophos, said: "Scammers have been known to bombard a PC with nuisance pop-up adverts, and then follow them up with messages that resemble system alerts to try and fool the unwary into downloading a 'solution' to fix the problem.

"You do not even have to be browsing the web to have these nuisance messages appear. Just being connected to the net can be enough."