Antivirus researchers have discovered what’s claimed to be the first computer Trojan to infect Apple Mac OS X computers. The malware, dubbed Leap-A, spreads via the iChat instant messaging system as a file called latestpics.tgz that infected machines send to contacts on an infected user’s buddy list. The malicious file, which poses as a set of pictures, is a compressed Unix shell program. The user is prompted for admin credentials to launch the malicious code, which is better described as a Trojan than a virus. Mac OS X users who do this will find their machines infected.