BleepingComputer.com: Hckpk: Malware In Disguise

Virus writers have been pummeling corporate networks and consumers with their latest trick -- malware that wraps itself in a variety of masks to evade detection by antivirus programs.

"It's a new way to disguise their malicious code,...Various malware authors are using HckPk, malicious code that's circulating in the Wild. Hackers can take the HckPk code and add it to their worms, which is akin to slipping a mask over someone's face...Sophos analysts calculate that HckPk accounted for more than half of all malware seen during February...