Credit:
Facebook is falling prey to a widespread phishing attack today that tries to steal your login and spam your friends.
I've got a number of messages in my Facebook inbox with links to "FBAction.net", a site that displays a fake Facebook login. Enter your details there, and it will spam all your friends with the same message and link. More worrying: you might get locked out of your account for a time until Facebook sorts out this mess.
There is no malicious payload with the attack, it seems: no virus is downloaded or any other nasties: it's simply a huge nuisance for Facebook users.