A vulnerability has been reported in Microsoft PowerPoint, which can be exploited to compromise a user's system. The vulnerability is caused due to an error when parsing certain strings in a specially crafted document.
Successful exploitation allows execution of arbitrary code. See this link (http://www.securityfocus.com/brief/254) for more detail. This is currently unpatched - do not open Powerpoint files sent to you from untrusted sources.
Update:
Microsoft have issued a Security Advisory to help you avoid the threat until a patch is released in the August update:
Microsoft Security Advisory (922970) (http://www.microsoft.com/technet/security/advisory/922970.mspx) :thumbsup: