This was posted on another site
I have received this several times in the past month myself. It looks similar but is not the one MSN uses. Do not fall prey to this! Do not fill this out!
It's a username and password Harvester . They can now use your username to send emails or viruses or whatever to anyone, anywhere, using your username details .
Please Do not touch it.
It is a popup disguised as a M$N Prompt to try and trick and decieve you
Close it , and sign out , then sign in again if by chance you have entered your info , go and change your password NOW!!!!!