Computer security firm Compurity has issued a warning about a new virus called Maccy.C that has been described as a "Windows cleaner".
It said Maccy.C tries to disable Windows software on infected computers, replacing it with a version of Mac OS X.
Compurity director Joss Bevet said: "Maccy.C is spreading through infected email messages and targeting machines running the Microsoft Windows operating system. Capabilities include the ability to uninstall the Windows operating system and replace it with a version of Mac OS X, the Apple operating system."
Irregular virus Antivirus software companies are warning PC users not to ignore the virus, which is carried as an attachment on an official-looking email, usually bearing a return address indicating it was sent by an administrator, computer support staff member, or manager. The email carries a message warning of an irregularity.
If the attachment is opened it installs a virus that uninstalls Windows, and opens a port on the user's computer. That port allows hackers to access the users PC and install a variant of the Mac OS X operating system based on Darwin. It is believed to resemble OS X 10.1.
The Antivirus Emergency Response Team rated Maccy.C a "high" threat – to Microsoft.