A new exploit called Evilgrade can take advantage of automatic updaters to install malicious code on unsuspecting systems, and your computers could be more vulnerable than you think.

Evilgrade is designed as a modular framework that accepts plug-ins capable of mounting attacks on a variety of software packages that employ their own auto-update procedures. Currently-supported targets include the Java browser plug-in, WinZip, Winamp, OpenOffice.org, the LinkedIn Toolbar, iTunes, and Mac OS X, among others. Still more plug-ins are liable to be developed in coming months.

The exploit works by pretending to be a genuine upgrade site and sending malicious code when your software was expecting a patch. The code might be anything, from a Trojan horse to a keylogger that intercepts passwords and user accounts.

Making use of the exploit isn’t quite as easy as just pressing a button. It requires a pre-existing “man in the middle” condition, in which an attacker sets up a fake Web host that can intercept traffic traveling between a client and a genuine server. But while ordinarily that might be pretty tricky to achieve, the recently-disclosed DNS security flaw leaves many sites wide open.