A recently discovered flaw in PowerPoint is being actively exploited, according to Microsoft. The company is warning people against opening any PowerPoint documents, or any Office document for that matter, coming from someone they don't trust. It's not possible to directly tell if you've been compromised by the flaw since there are no external signs. Because of this, along with the flaw offering total system compromise, it has earned Secunia's "Extremely Critical" rating.
The flaw, which does not have a fix yet, affects several versions of PowerPoint from Office 2000 up to Office 2003 and Office 2004 for the Mac. There's no mention of what Microsoft counts as "actively exploited," though we've seen in the past that flaws which are very severe but not exploited often don't get much attention from them. Therefore, we can at least assume this flaw has gotten to the point where it's more than just a few isolated incidents. Of course, we should all know better than to open any files from people we don't trust.