Like MacDefender, MacSecurity and MacProtector, the latest version – called Mac Guard – is being spread by linking it to popular internet search terms. Unlike its predecessors however, Mac Guard does not require a user's permission to be installed, according to security firm Intego.
In all cases, the malware re-directs Mac users from legitimate websites to fake websites, which tell them their computer is infected with a virus.
The user is offered fake security software, with the aim of getting the user's credit card information.
Intego has issued a warning about Mac Guard and advises Apple Mac users to disable a setting in the Safari browser that lets "safe" files be installed automatically.
Intego and Apple have also published guides on how to avoid infection and how to remove the malware from infected machines.
This story was first published by Computer Weekly