A nasty Trojan that first hit Mac users just over a year ago has returned with sharpened teeth, a security company has revealed.

According to Mac-only security company Intego, the latest variant of RSPlug, known as RSPlug.E, has been discovered by the company on porn Web sites masquerading as a missing ActiveX plug-in needed to play a video.

As with its many equivalents in the Windows world, the software tries to trick users into installing it after complaining of a "missing Video ActiveX Object", which turns out to be where the program starts its install routine.

Trying to cancel the install at this point by clicking cancel prompts the malware to deliver the message, "Please install new version of Video ActiveX Object". The only way out at this point is to exit the browser.

What users get for their naivety is a DNS hijacker, capable of redirecting web address requests to any website the criminal desires, including phishing websites.

"Mac users are pretty unsavvy as far as security is concerned," said Peter James of Intego, who reckoned that many still Mac users run their computers unprotected, despite numerous warnings.

"As Mac market share is increasing, malware is increasing proportionately," he said.

Intego, of course, admits that it has a vested interest in publicising Mac malware, including drive-by Trojans such as RSPlud.E. Nevertheless, the fact that Mac users are now facing the sort of Trojan programming threats regularly experienced by PC users should alert them to the importance of the issue.

As PC Trojans go, the programming features of RSPlug.E look fairly basic. PC malware is more highly evolved and usually cleverer. But a programmer - probably a Russian - with knowledge of OSX had taken time to create a Trojan that hits Macs instead of PCs, James pointed out.

One curiosity is that one of the key files installed by the program actually bears the name of Intego itself, a provocative reference to the company's publicising of previous versions of the Trojan, and possibly a warning too.

Intego warns Mac users not to download software form unknown sources - advice PC security vendors were handing out to Windows users five years ago.