There is a zero day security exploit for the Adobe PDF Reader that is currently out in the wild and for which there is no patch. It exploits a vulnerability in Reader’s Javascript implementation.
Details here.
If you must use Adobe Reader you should disable Javascript until this is fixed.
- On Windows, launch Adobe Reader and go to Edit > Preferences > JavaScript and uncheck Enable Acrobat JavaScript.
- On a Mac, launch Adobe Reader go to the Adobe Reader menu > Preferences > JavaScript and uncheck Enable Acrobat JavaScript.
Alternative free PDF viewers are Preview.app on Mac (included with OS X), and Foxit Reader on Windows.