It was released today on several sites that PDF files, and their corresponding readers have a critical vulnerability that would allow an attacker to compromise a computer, even with many of the normal protections in place that block things such as Javascript.
Foxit Reader (NMP Recommended) and Adobe Reader both have fixes for this vulnerability. Go to http://www.foxitsoftware.com/pdf/reader/ and download and install the latest version.
For Adobe Reader users, make the following preference change:
From the Edit menu go to: Preferences -> Categories -> Trust Manager -> PDF File Attachments and then uncheck ‘Allow opening of non-PDF file attachments with external applications.’
This is a problem that could possibly affect all platforms and Operating Systems, whether Windows, OS X, or Linux.