Finnish security company F-Secure released patches for its flagship Windows and Linux anti-virus line Thursday to fix flaws revealed by an independent researcher.

The bugs in 23 editions of F-Secure Anti-Virus, Internet Gatekeeper, and Internet Security affect how it parses .zip and .rar compressed files, according to the researcher, Thierry Zoller, who works for an unnamed Luxembourg security firm.

Maliciously crafted .zip files can be used to create a buffer overflow on PCs defended with F-Secure titles; after that, hackers could load their own code onto the compromised machine. A second flaw can be exploited with specially made .zip or .rar files to hide malicious code from the anti-virus scanning engine, giving users a false sense of security and attackers a way to sneak stuff past protection.

F-Secure dubbed the flaws "Critical," and rolled out fixes Thursday. Patches can be downloaded from the Helsinki-based company's FTP servers. (F-Secure Anti-Virus 2004/2005/2006, Internet Security 2004/2005/2006, and Personal Express 6.2 and earlier will automatically retrieve the fixes.)

"Our guidance is the same as for patches from any other vendor: Patch now before someone figures out how to exploit the vulnerability," F-Secure's director of anti-virus research, Mikko Hypponen, wrote on the company's Web site. "At the moment we are not aware of any attacks that would have used this vulnerability."

F-Secure's rapid patch posting was in stark contrast to Symantec, which was hit with a bug that affected more than 60 of its enterprise and consumer anti-virus products on Dec. 21, 2005. Symantec only finished patching the last of the bunch on Wednesday, Jan. 18.