Online criminals are making millions of pounds by forceful computer users to download fake anti-virus software, internet security experts argue.
Symantec says more than 40 million people have fallen prey to the "scareware" scam in the past 12 months.
The download is usually risky and criminals can sometimes use it to get the victim’s credit card details.
The firm has acknowledged 250 versions of scareware, and criminals have idea to earn more than £750,000 each a year.
Franchised out
Scareware sellers use pop-up adverts intentionally designed to look valid, for example, using the same typefaces as Microsoft and other well-known software providers.
They often appears when the user is switching between websites, and falsely warn that a computer’s security has been compromised.
If the user then click on the message they are pointed towards another site where they can download the fake anti-virus software they apparently need to clean up their computer – for a fee of up to £60.