If you are running Adobe Acrobat version 7 or later, you are in danger of being exposed to malware infection even if you never actually opened an infected file. There's an unpatched bug in Adobe Acrobat that allows some specially-made PDF to crash Acrobat and inject its own code into your system and install a malware. This bug has been known for some weeks already (and some exploits using this bug has been reported) but Adobe has not yet released a patch that will fix this. What makes this bug very dangerous is the fact that it can trigger a malware infection even if you do not open a pdf file. The best thing to do now is to completely uninstall Adobe Acrobat an wait for the patch before using it again.