Microsoft has teamed up with the Attorney General in Washington to file lawsuits against companies that use scare tactics to convince people that their computer is infected in order to sell software.

For anyone who uses the internet extensively pop-ups that tell you 'your registry may be corrupted' and tries to con you into downloading a scan that will advise on buying software is a familiar site.

But for thousands of people this 'scareware' is enough to prompt them to buy software they almost certainly don't need.

Blatant rip-off

Attorney General Rob McKenna – calling the practice a "blatant rip-off of consumers" – said that users are "duped into downloading a fake scan (of the computer) and then duped into paying for software they don't need".

"We won't tolerate the use of alarmist warnings or deceptive 'free scans' to trick consumers into buying software to fix a problem that doesn't even exist," said McKenna.

"We've repeatedly proven that internet companies that prey on consumers' anxieties are within our reach."