Adobe and Microsoft today separately issued updates to fix critical security vulnerabilities in their products. Adobe pushed out fixes for security issues in Acrobat, Adobe Reader and its Flash Player plugin. Microsoft released seven patches addressing at least a dozen security holes in Windows and other software, although it failed to issue an official patch for a dangerous flaw in its Internet Explorer Web browser that attackers are now actively exploiting.Adobe patch here (effects Windows, Mac, and Linux).
Microsoft patches via Windows Update (you have to use Internet Explorer here).
Also, Internet Explorer users really need to get to version 9 or higher, because Microsoft did not patch the IE hole that is currently being exploited. This is a problem for folks still on Windows XP, because that's End Of Life and there are no more security patches, and IE 9+ doesn't run on it. You can use the Microsoft workaround or better yet install Linux. Ubuntu has some wretched advertising (one dare not call it "spyware" but one wants to), and so I recommend Linux Mint. Should run fine on hardware currently hosting XP.
UPDATE 9 January 2013 16:32: It seems that Microsoft's workaround is not much use. Windows XP users who don't want to switch to Linux should use Firefox or Chrome instead of Internet Explorer.