I recently upgraded to Bitdefender Internet Security 2012 from 2010, because the old version was messing with Firefox. Since I've upgraded Live Messenger crashes every time it tries to sign in. I immediately get the message "Windows Live Messenger is not responding".
It does work in Safe mode, and when Bitdefender is shut down (it crashed one time, and then I tried WLM, it worked) So I know the problem is with Bitdefender.
I use Windows 7 (32 bit) and WLM 2009 with Messenger Plus.