Antivirus company Sophos says the first "real virus" that targets Apple's Mac OS X operating system has been spotted online, reports Forbes. Appropriately enough, it was a type of virus called a worm. A Mac rumors website first reported a sighting on Feb. 13, in the form of a file called latestpics.tgz, supposedly consisting of screenshots of the Leopard Mac OS X 10.5; however, despite displaying a JPEG icon when click on, it was an executable file.

"OSX/Leap-A is programmed to use the iChat instant messaging system to spread itself to other users. As such, it is comparable to an email or instant messaging worm on the Windows platform. Worms are a sub category of the group of malware known as viruses," Macworld quotes from a Sophos statement.

Apple claimed in a separate statement that the worm, dubbed Leap-A, "is not a virus, it is malicious software that requires a user to download the application and execute the resulting file." It urged users to accept files only from "vendors and websites that they know and trust."