A worm that affects computers running Apple's Mac OS X operating system is circulating on the Internet, according to antivirus software makers.

The worm, Leap.A, spreads through the iChat instant messaging client and causes applications to run improperly, according to warnings posted on the sites of several antivirus software makers.

The discovery of the Leap.A is noteworthy because Mac OS X is generally regarded as being free of the many viruses and worms that can afflict computers running Microsoft Windows operating system. However, Leap.A is not deemed a major threat, according to Symantec.

Leap.A is sent from one computer to another as an attachment, called latestpics.gz, to an iChat message. The worm affects computers running Mac OS X version 10.4, Symantec said. When a user saves this attachment and clicks on it, a file called latestpics is created.

While Leap.A is relatively easy to remove from an infected system, Symantec recommended that users reinstall the operating system on their computers once they have been disinfected.