Update your Flash Player installations at http://www.adobe.com/go/getflashplayer
. It's the usual reason... potential pwnage of your system via a malicious Flash/Shockwave thingie. This reportedly affects Linux and Mac as well as Windows.
If you have additional web browsers besides Internet Explorer, don't forget to visit once with each browser to ensure that all of them have the updated version of Flash Player.
This would also be a good time to check your Windows systems with Secunia's vulnerability checkup. They have browser-based and installable versions at http://secunia.com/vulnerability_scanning/personal/
. Are you among the 2% whose system actually is
[Picard] Make it so. [/Picard]
Also, if you haven't fully enabled your Data Execution Prevention on WinXP/Vista/7, that's easy and worthwhile
. And if you have Vista, enable IE7's own dedicated DEP
while you're at it.*
*If you have IE8 beta or RC1, DEP is already enabled