Spanish Prisoner scam on the rise
To recap: in the Spanish Prisoner scam, someone writes to you claiming to be a prisoner in a Spanish prison (the scam is said to goes back to the 1500's). If you send bail money, riches will be yours once he returns to freedom.
In the modern variant, the offer either arrives via random spam, or targeted directly to you through the compromised email account of a friend.
The latter form is the most insidious. The email actually comes from someone you know, claiming to be in dire straights of some sort or another. Typically your friend is traveling abroad, the email will say, and has been robbed of cash, credit cards, and ID. You are begged to send cash as quickly as possible so your poor friend doesn't wind up jailed as a vagrant or some other terrible thing.
If you're sharp, you might notice that your friend isn't calling you by your name. Or you might remember that your friend isn't traveling anywhere at all, and in fact you had poker night with them just last night.
If you're a little bit slow on the uptake, you might actually send some money. If that happens, expect to get requests for more (oops, too late, he got arrested for vagrancy and now needs bail money).
The requests for money will continue until you catch on or run out of money to send.
For a good account of the scam, read Gadi Evron's article Facebook Scam: I'm Stranded In London. Send Money!
So remember to be on the lookout. If you get email from a friend asking for emergency money, always double-check via some other channel. A phone call is best.
And if you're the one whose email, facebook, or other account has been used for a scam like this, be sure to contact everybody on your contacts list and warn them. Chances are, the scammer has been hitting every name on the list.