A new variant of the Koobface worm is targeting Facebook members. You
could receive a message that looks like a Facebook message, and has a link regarding
a video, and asks you to update your Adobe Flash Player. This is the
malware. Do not click in the link in the email. Log into your
Facebook account by typing www.facebook.com
directly into your address bar, and see if the message is in your actual
account.
You can read about this worm here:
http://blogs.pcmag.com/securitywatch/2009/03/new_koobface_variant_preys_on.php