Have you got Flash player 9,0,115,0 or earlier? Check. No, really, do it now. These versions are apparently vulnerable to an exploit that can put malicious software on your system, including keyloggers that are set to swipe MMO passwords and credentials, like your World of Warcraft account. This is happening right now, according to Symantec.
The latest update, version 9,0,124,0 is apparently not vulnerable to the exploit according to Adobe. You should probably get that version now, if you trust Adobe's information. If you trust Symantec's alert, only versions 115 and 124 are vulnerable, and this is a new exploit, and not the one that Adobe is talking about. If you want to play it safe, go plug the No-Script add-on or Flashblock into your Firefox browser, and breathe a huge sigh of relief until everyone gets their story straight (but check your system for malware first, okay?)
Update: Symantec and Adobe agree that 124 is not vulnerable. If you have any other version, you should upgrade.