My comments and further explanation on this topic
This article in Facebook’s blog touches on a very common risk that can affect any social-networking site and user community. It mainly talks of the “money scam” which is really similar to the common “Nigerian” or “419” scam that many of us have encountered through the spam that comes in our mailboxes.
In the social-network version, a fraudster “sets up shop” on a Facebook or similar site and takes over a user’s account. They will then message the user’s social-network friends claiming that they are in another land and out of money. This will be via a message on the Wall or a direct message via the Inbox or a Chat session. They will typically require the friends to wire a huge amount of money to the scammer.
If you do receive one of these kinds of contacts from your friends via a social-networking Website, make a call by regular telephone to the number that you know the friend (or a person that you are sure knows them well such as their spouse / partner, child or employer) can answer such as their home or mobile number. Here, I would prefer to make a voice call rather than use text messaging. Then you can ascertain whether it is the friend who is in need or simply a scam taking place. As well, confirm the situation with mutual contacts. If the friend’s account is being compromised, tell them to change the account’s password immediately. Sometimes, companies like Facebook can lock down a compromised account and e-mail the account holder about what is going on. Then they advise the account holder to change their password immediately.
As well, know what resources do exist in your social-networking service for reporting compromised user accounts and be ready to identify “out-of-character” messages, links or pictures posted up on these services by your friends. For Facebook users, the link is http://www.facebook.com/help.php?page=420 .