Windows Vista is hyped to be a most secure Operating System till date. It has built in antivirus tool called Windows Defender.
But, what can you say when Windows Vista's security falls with its own "Animated cursor exploit" that is known to Microsoft since December 2006! The ANI exploit is a bug in the way Windows renders animated cursor files that can allow execution of arbitrary code under the privileges of the user that downloaded the malicious file. Here is an example with Video - how Windows Vista falls and crashed with this exploit.
Microsoft has released an update about this, and a patch may be ready by this evening.
Update 1 # Zdnet had reported that more than 150 sites had already been infected and counting...
Update 2 # And now Firefox too had this flaw.