This one's been around, in various forms, for decades. Before the Internet they used faxes, telegrams, and business letters. Googling "Nigerian Scam" turns up 20,300 hits; top of the list is Nigeria - The 419 Coalition Website; here's their summary:

The Scam operates as follows: the target receives an unsolicited fax, email, or letter often concerning Nigeria or another African nation containing either a money laundering or other illegal proposal OR you may receive a Legal and Legitimate business proposal by normal means. Common variations on the Scam include "overinvoiced" or "double invoiced" oil or other supply and service contracts where your Bad Guys want to get the overage out of Nigeria; crude oil and other commodity deals; a "bequest" left you in a will; "money cleaning" where your Bad Guy has a lot of currency that needs to be "chemically cleaned" before it can be used and he needs the cost of the chemicals; "spoof banks" where there is supposedly money in your name already on deposit; and "paying" for a purchase with a check larger than the amount required and asking for change to be advanced. Or the victim will just be stiffed on a legitimate goods or services contract...the variations are very creative and virtually endless.

At some point, the victim is asked to pay up front an Advance Fee of some sort, be it an "Advance Fee", "Transfer Tax", "Performance Bond", or to extend credit, grant COD privileges, whatever. If the victim pays the Fee, there are many "Complications" which require still more advance payments until the victim either quits, runs out of money, or both. If the victim extends credit etc. he may also pay such fees ("nerfund" etc.), and then he is stiffed with NO Effective Recourse.

The Nigerian Scam is, according to published reports, the Third to Fifth largest industry in Nigeria....