Alert over "extremely critical" Word flaw

An "extremely critical flaw" in Microsoft Word 2000 is currently being exploited by malicious attackers, which could lead to remote execution of code on a user's system, security researcher Secunia advised on Tuesday.

The vulnerability affects systems running Windows 2000 and occurs when processing malicious Word 2000 documents, according to Secunia's security advisory.

Security company Symantec, which several days ago detected the exploit, Trojan MDropper.Q, noted that it uses a two-step attack.

Trojan MDropper.Q exploits the Microsoft Word vulnerability to drop another file, a new variant of Backdoor.Femo, according to a security advisory by Symantec.

Symantec's advisory stated: "As with other recent [Microsoft] Office vulnerabilities, documents incorporating the exploit code must be opened with a vulnerable copy of Microsoft Word 2000 for it to work. As such, it makes the vulnerability unsuitable for the creation of self-replicating network worms."

Microsoft has not yet issued a patch for the vulnerability, and users are advised to forgo opening untrusted documents.

This latest exploit of an Office vulnerability follows on the heels of another, similar malicious attack in June. In that particular case, users' systems would become infected when opening a malicious Excel document called "okN.xls". That malicious file contained the Trojan horse Mdropper.J, which then dropped the Booli.A program on a user's system. Booli.A would then download more malicious files to the user's PC.

Dawn Kawamoto writes for CNET News.com