The Security Mentor

Open a .PPT file prepared by a malicious person, and they can take over your computer.

Until Microsoft fixes Powerpoint and until you install the fix, avoid Powerpoint files from unknown sources and scan others with your antivirus program: it may detect boobytrapped files.
UPDATE:
According to one source this problem doesn't affect the Powerpoint Viewer program. If you don't need to edit the file then a great workaround is just not to open it in Powerpoint (which unfortunately is what will happen if you double-click it).