They have discovered the first virus for the Apple Mac OS X platform "in the wild," meaning one that has escaped the confines of an experimental laboratory and is meant to cause harm. The worm is called Leap-A or Oompa-A, and it spreads via the iChat instant-messaging system, forwarding itself as a file called latestpics.tgz to contacts on the infected users' buddy lists.
"Some owners of Mac computers have held the belief that Mac OS X is incapable of harbouring computer viruses, but Leap-A will leave them shell-shocked, as it shows that the malware threat on Mac OS X is real," Sophos senior technology consultant Graham Cluley said in a statement.
"Mac users shouldn't think it's okay to lie back and not worry about viruses," he added.
Virus experts at McAfee have confirmed its existence, and say it runs only on PowerPC-based machines running Mac OS X.