Microsoft has issued a security advisory about a zero day flaw that affects its Word application.

The issue affects Word 2000, 2002, 2003, Word Viewer 2003, Word 2004 for Mac, Word 2004 v. X for Mac and Works 2004, 2005, and 2006. It allows hackers who form malformed strings within documents to execute code on a target PC.

“Do not open or save Word files that you receive from un-trusted sources or that you receive unexpectedly from trusted sources,” warns the advisory.

“This vulnerability could be exploited when a user opens a specially crafted Word file.”

Once used the flaw will only allow local access to the compromised system, so damage to other hardware on the network should be limited.

The company says that it is working on developing a patch for the problem, but that nothing has been released as yet.