Cyber attackers exploiting Word flaw

A yet-to-be-patched security hole in multiple versions of Word is being exploited in cyber attacks, Microsoft has warned.

The attacks are "limited", according to the software giant. It said it is developing a security update that addresses the vulnerability.

The vulnerability is similar to previous so-called zero-day flaws that have hit Office applications in recent months. An attacker could rig a Word file in such a way that he would gain complete control over a vulnerable PC when the file is opened, Microsoft said in an advisory.

An attacker could exploit the flaw by hosting a website with a malicious Word file or send an email with the file as an attachment. In all cases the target would have to open the file to be compromised, Microsoft said.

Security experts have said the limited scale attacks are the most dangerous. Widespread worms, viruses or Trojan horses sent to millions of mailboxes are typically not a grave concern since they can be blocked. Instead, especially for businesses, targeted Trojan horses have become the nightmare scenario as they can fly under the radar.

The latest Office vulnerability affects Word 2000, Word 2002, Word 2003, Microsoft Word Viewer 2003, Word 2004 for Mac, Word 2004 v. X for Mac, and Works 2004, 2005, and 2006, Microsoft said. As a way of protection, Microsoft suggests not opening or saving Word files from unknown sources or which arrive unexpectedly.

Joris Evers writes for CNET News.com