Fixing a glitch whose only known ill effect was that it forced users to restart Internet Explorer hardly ranked at the top of Microsoft's to-do list. But that was before a UK-based security researcher named Stuart Pearson pointed out a way that bad guys could exploit the hole to take over affected computers. With the exploit code floating around the Web, it was only a matter of time before somebody created malware that employed it as an infection mechanism. You could get infected by visiting a site that has a contaminated banner ad in the background, by opening an HTML e-mail with the malware, or by viewing a tainted attachment.

The flaw involves the way IE handles JavaScript--a common Web programming language. IE versions 5.5, 6, and 6 Service Pack 1 running on Windows 98 through XP Service Pack 2 are affected. The research company where Pearson works, counterintuitively called Computer Terrorism, has posted a self-test site where you can check whether your PC is vulnerable. A successful test means your PC is vulnerable, and the calculator in Windows appears on screen to indicate your system is at risk.

Given the newly discovered (and more dire) potential consequences of the breach, Microsoft has released a security warning about the problem. But as we went to press, the company had not released a patch to fix things yet. The company does identify three workarounds. One option is to disable JavaScript in IE or to set up the browser to prompt you for permission before it executes any JavaScript. For details on the various workarounds, click here, scroll down to General Information, click Suggested Actions, and then click Workarounds.

Graphics Glitch

Microsoft has also patched a pair of critical security holes in the way Windows displays images using the Windows Metafile (WMF) and Enhanced Metafile (EMF) formats, which are used to transfer images between Windows applications--when cutting and pasting graphics between Office apps, for example. The security gaps appear in the portions of the Windows operating system that handle graphics rendering either for on-screen display or for printing.

By sending a corrupt WMF or EMF file containing a bad command to your Windows' graphics system, an attacker could easily crash the OS and then run a rogue program to take control of your computer. Typically, the hacker must trick you into either clicking an infected image file or viewing an HTML e-mail message that has corrupted graphics embedded in it. But a bugged file could infect your system via the preview pane in Microsoft's Outlook or Outlook Express e-mail program. The flaw affects systems running any version of Windows between 2000 and XP SP2. You can download the patch here.