Microsoft's Malware Protection Center has posted an article about a new Mac backdoor called Olyx that they have "discovered" in a package also containing Windows malware. Intego spotted this backdoor some time ago, and added it to VirusBarrier's malware definitions on June 30, as OSX Backdoor OSX/Olyx.A. There is little threat to this malware, as it is not found in the wild in any form that can be installed on Macs.
Intego regularly finds malware of this type, which is neither well designed, nor able to be easily installed on Macs. Intego's Virus Monitoring Center adds this malware to its malware definitions, ensuring that Mac users are protected in case such malware does get added to effective payload, such as the MacDefender fake antivirus or other Trojan horses. We don't publicize such malware by issuing security alerts, because the threat is not serious enough.