Chinese-language blogs are detailing a zero-day vulnerability in Microsoft Works, the company's lower-end office productivity suite, according to security vendor McAfee.

The vulnerability is within an ActiveX control for the Works' Image Server, wrote McAfee analyst Kevin Beets. A PC would need to visit a Web site engineered to exploit the flaw, Beets wrote.

A zero-day flaw is a software vulnerability that has become public knowledge but for which no patch is available. It is particularly dangerous since users are exposed from day zero until the day a vendor prepares a patch and notifies users it is ready.

Proof-of-concept code was posted on a Chinese blog showing how the problem could cause Windows to crash, Beets wrote. Then, a few hours later, a working exploit appeared, which could allow malicious code to run on a machine.

ActiveX is Microsoft's technology that lets Web site designers add extra functionality to Web pages or allows different applications to access the same software component, such as a spell-checker. But ActiveX controls have also been employed by hackers in order to trick people into downloading malicious code.

As with most ActiveX controls, users will get a warning asking whether they want to download it or not, Beets wrote, but the vulnerability is "easily exploitable" once the control has been downloaded. McAfee tried it out using Windows XP Service Pack 2 and Internet Explorer 7.

One way to halt the attack is to block the particular ActiveX control, Beets wrote. Microsoft has instructions on its Web site for this procedure.

The company did not have an immediate comment as of Friday morning.