Microsoft warns of new PC threat

A new vulnerability has been detected in PCs running Microsoft's Excel spreadsheet and PowerPoint presentation programs, which allows a specially crafted macro to avoid detection and run malicious code on a victim's machine.

The software hole allows a malformed macro--a mini-program that runs within an application--to escape the security warnings built into Excel and PowerPoint, so that a computer user can unknowingly run infected macros when opening a spreadsheet or presentation.

"Macros have their own programming language and can automate the tasks that a user would normally do," said Mark Read, security analyst at MIS Corporate Defence Solutions. "There is the potential for them to release code that could be very dangerous--it doesn't matter what the application is."

The macro could be programmed to take any action that the owner of the PC could take. According to Computer Emergency Response Team at Carnegie-Mellon University, this could include reading, deleting or modifying data; modifying security settings; sending e-mail or posting data on Web sites.

The dangerous potential for macro viruses was demonstrated on a massive scale two years ago with the Melissa virus. The macro virus propagated in the form of an e-mail containing an infected Word document as an attachment. When a person opened an infected document with Microsoft Word97 or Word2000, Melissa immediately executed itself if the macros were enabled.

"We've had macro viruses around for a long time--since Microsoft built the angle into its products," Read said. "Microsoft added warnings giving the user an option to back out, but now this safeguard has been removed through this new vulnerability, creating new potentials for" virus writers.

Microsoft issued a security bulletin about the Excel and PowerPoint vulnerabilities on its site, but the company is refusing to make any further comment.

Staff writer Wendy McAuliffe reported from London.