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No sooner had Microsoft issued a massive set of security patches for its software than hackers started posting code showing how to exploit one of the flaws.

The proof-of-concept code, posted Wednesday to the Milw0rm Web site, exploits a bug in the Microsoft Works file converter software that is part of Office 2003 and can be used to run unauthorized software on a victim's computer.

The flaw also affects Works 8 and Works Suite 2005. To fall prey to the attack, a victim would first have to open a malicious Works attachment.

Hackers have uncovered many of these file-format bugs in recent years and they are generally not used in widespread attacks. In fact, security vendor Symantec predicts that we'll see fewer of these attacks in the months ahead as online criminals increasingly rely on browser bugs to do their dirty work.

"The bad guys, they're looking for different ways to trick people," said Wayne Periman, director of development with Symantec Security Response. "The popular method of choice is to exploit plugins in browsers right now."

Still, Periman expects criminals to try out this latest attack code. "It's so simple," he said. "All you have to do is get someone to open the document."

The software vendor released 11 sets of patches this week, fixing 17 flaws in its products, but this is the first exploit code to pop up following the updates. A second program exploiting one of these vulnerabilities -- this one in an ActiveX control used by the Visual FoxPro database -- was posted to Milw0rm in September, months before Microsoft patched the issue.