Security consultant Sophos is warning of the appearance of money-grabbing Trojan Horse malware aimed at Macs

The firm isn't being alarmist with news of the Imunizator Trojan, which makes false claims that Macs have privacy problems as part of its attempt to install itself. Sophos advises users not to panic.

The Trojan, also known as Troj/MacSwp-B, tries to scare Mac users into purchasing unnecessary software by claiming that privacy issues have been discovered on the computer.

"Windows users are no stranger to scareware like this, but it is rarer on the Mac.  Nevertheless, the discovery of this Trojan horse does follow fast on the heels of other malware that has been identified on Mac OS X in recent months," said Graham Cluley, senior technology consultant for Sophos.  "Cybercrime against Mac users may be small in comparison to Windows attacks, but it is growing. Mac users need to learn from the mistakes made by their Windows cousins in the past and ensure that they have defences in place, are up-to-date with patches and exercise caution about what they run on their computer."

Sophos experts note that the new Trojan horse is closely related to another piece of Mac scareware, MacSweeper, which was being deployed in an attack via online adverts on ITV.com and the website of the Radio Times last month.

"It's not unusual to see hackers repackage their malware in a variety of disguises to try and sneak it past anti-malware software," explained Cluley.

Earlier this year Sophos published its annual Security Threat Report, which described how financially motivated hackers had targeted Macs for the first time in 2007.