A newly disclosed flaw in Microsoft Word could let malicious hackers take control of victims' computers by sending them e-mail with a Word document attached.
Microsoft Corp. informed computer users of the problem Tuesday, though the company classified it as a security "advisory." That makes it a less urgent warning than other security disclosures, though the company is investigating attacks that exploited the vulnerability.
As of Wednesday evening, the company had not released a patch to fix the problem.
The vulnerability affects versions of Microsoft Word sold from 2000 through 2006. Microsoft Word 2007, which is currently available only to businesses, is not vulnerable, the company said.
To fall prey, a computer user would have to open a Word document attached to an e-mail. Microsoft advised people not to open or save attachments from unknown correspondents. Security experts consider that standard e-mail advice under any circumstances, but Microsoft also suggested rejecting unsolicited attachments even from friends and colleagues.
This vulnerability appeared no more dangerous than other flaws that have emerged previously in Microsoft Office applications, said Dan Hubbard, vice president of security research at Websense Inc.
Even so, the threat is worth taking seriously, said Justin Bingham, chief technology officer for network monitoring company Intrusic Inc.
He noted that it would be very easy for a con artist to call someone in a company, state a legitimate-sounding pretense _ posing as a vendor or a jobseeker, for example _ and then send an e-mail with an benign-seeming Word attachment that exploited the security hole.
"The gravity of this problem is very big," he said. He added that when Microsoft issues a patch for the security hole, companies should install it immediately rather than waiting until their next regularly scheduled update.