You know, I just spent a week at the RSA Security Conference, courtesy of Avast! (Thank you again!). And pretty much every day there was a session showing how the social networking sites were the greatest things ever for identity thieves, phishers, email baddies, .. There were even some discussions about how easy it was to get people to give up their passwords for "good reasons" in such a setting. So if you want to use them to support avast!, even through the "Like" button, be sure it is only as a reader of the information, or anonymous commenter, not as a supplier of information about yourself. Don't create an account for this purpose. If you do have an account for other purposes, or need to register, provide as little information as possible and lie when you can, using a disposable email address.
FaceBook is not your friend, in spite of all the "friends" you may have there.