Ugh! I had just been targeted by the Twitter Virus!!!
This particular virus sends direct messages from a Twitter account to people who follow that account, telling the recepient that he or she appears in an interesting video. The message also helpfully includes a link to the suspect video. But the video link goes to an imitation Facebook page where you are prompted to enter your Facebook login information. Also, as soon as you click the link, the virus begins trolling your followers list, resending itself to continue the hack.
If you get one of these messages, DO NOT OPEN THE LINK. I would also let the sender know that their Twitter account seems to be hacked. That's how I found out later that my Twitter account was hacked - a very nice person told me about a message that I supposedly sent them.
If you do click on the link or your Twitter account is otherwise hacked, I suggest you take the following steps: