I like and use mdx. But I wouldn't rely on any program or site that checks if you are blocked. Ms fixed that a long time ago.
http://www.mess.be/msnmessengerfaq/i...Messenger.html. Mdx works for me when people sign in as offline. Signing in as offline is different I think. I tested it with a friend and it worked but I don't know how accurate it is or isn't worked though when we tested it.