Security experts are warning users to be on the lookout for a new rash of fake anti-virus scams.

The rogue security applications are disguised as legitimate antivirus tools, often offering false scans or creating pop-up windows which warn users that their systems are 'infected'.

Believing that the security program is legitimate, the user pays money for the phoney software.

"Losing $50 for a fake program is bad enough, but victims should be worrying about losing much more," wrote Trend Micro technical communications team member Macky Cruz in a blog entry.

"Once hackers get their hands on credit card information there is no telling what risks are in store for victims."

One piece of malware, known as WinAntispyware 2008, alters the user's desktop and system preferences to display alert messages and instigate system scans in an attempt to fool the user into purchasing the non-functioning security tools.

New rogue security applications have also been discovered in recent days by Sunbelt Software. Among the names being used by the applications are Windows AntiVirus, Windows AntiVirus 2008, AntiVirus Lab 2009 and Antispyware Pro XP.

The US Computer Emergency Response Team is advising users to avoid the scams by installing only trusted security software from known vendors.

Users are also advised to follow general best practice such as not following unsolicited links or downloading software from untrusted sources.