OSX.Leap.A is a new trojan horse that targets the Macintosh OS X and spreads via iChat Instant Messenger program.

OSX.Leap.A - New Mac OSX Trojan Horse
http://secunia.com/virus_information/27059/osxleap-a/
http://secunia.com/virus_information/30445/osx.exploit.launchd/
http://www.sarc.com/avcenter/venc/data/osx.exploit.launchd.html
http://www.theregister.co.uk/2006/02/16/mac_os-x_virus/

OSX.Exploit.Launchd is a Trojan horse that exploits the Apple Mac OS X LaunchD Local Format String Vulnerability (as described in Security Focus BID 18724). It provides root access on the Macintosh OSX version 10.4.6 or earlier.