Introduction :
Flaws in the way F-Secure software handles ZIP and RAR data compression archives could allow an attacker to execute remote code on users' systems and also to bypass F-Secure's antivirus-scanning capabilities.

Details :
I found mutliple vulnerabilities within various AV Engines, F-Secure are the first to actually publish a real advisory, others fixed the bugs silently or put a small notice in a change_log. I will however not publish more details about the findings as of yet, there are too many AV engines vulnerable to similar issues and I am going to wait until most of them have patched the flaws until I exactly dislclose my findings.
http://www.f-secure.com/security/fsc-2006-1.shtml

Rain Forest Puppy once defined a "Responsible Disclosure Practice", I adhere to it.
[Update]
The Story has been posted on SecurityFocus, News.com, Washington Post, Heise, Suedeutsche, ZDnet, Computerworld, and various others. Special Thanks to Mikko for giving me Credit.