An anonymous security researcher claims to have developed a worm capable of delivering a malicious payload to fully-patched Mac OS X systems.

A posting on the Information Security Sellout blog insists that the worm proves that Apple computers are as vulnerable to malware as Windows-based PCs. 

The blog is written by a group of anonymous researchers using the name 'Infosec Sellout'.

The researcher responsible for the post claimed to be developing the worm for a client, and said that no proof-of-concept or related details will be published. The author claims that the client does not plan to use the worm for criminal purposes.

The author has not yet notified Apple of the bug, but plans to contact the company "eventually".

The vulnerability apparently exploited by the worm lies in OS X's MDNSResponder networking component.

When exploited, the author claims that the worm has the capability to execute code at root level, allowing an attacker to install malware on the target system.

"While it is nothing special compared to Windows-based malware it does prove a point," wrote the researcher. "Apple computers are just as susceptible to malware as Windows-based ones."

The Infosec Sellout researcher is not the first person to attempt to prove such a point.

A virus for Apple's iChat application first appeared in February 2006, followed by another targeting OS X's Bluetooth software. Nine months later a third virus, dubbed OSX.Macarena, was found. 

None of these viruses was able to record more than 50 infections, and no malware installations were ever reported.