Windows users running older version of Adobe Reader (9.4.6) are currently vulnerable to targeted attacks.  The vulnerability also exists in Adobe Reader X, but there are other ‘built-in’ anti-exploitation measures that reduce the risks for those users.

According to Adobe:

I’d like to take this moment to encourage any remaining users still running Adobe Reader or Acrobat 9.x (or worse, older unsupported versions) to PLEASE upgrade to Adobe Reader or Acrobat X. We put a tremendous amount of work into securing Adobe Reader and Acrobat X, and, to date, there has not been a single piece of malware identified that is effective against a version X install. Help us help you by running the latest version of the software!

You can download Adobe Reader X here.