Someone in the Syrian telcoms authority is running a clumsy man-in-the-middle attack against Facebook; activists who try to access the site in Syria using SSL get a message saying that the certificate doesn't match.
The attack is not extremely sophisticated: the certificate is invalid in user's browsers, and raises a security warning. Unfortunately, because users see these warnings for many operational reasons that are not actual man-in-the-middle attacks, they have often learned to click through them reflexively. In this instance, doing so would allow the attackers access to and control of their Facebook account. The security warning is users' only line of defense.A Syrian Man-In-The-Middle Attack against Facebook