Nigerian Letter scams have been around for ages. Originally, these scams originated in Nigeria, though today they come from just about anywhere.
To create the scam, criminals send out thousands of letters that appear to be from a banking or legal official. The letters claim there is a large sum of money that can only be released to a relative of some deceased member of royalty (often, a person that was persecuted by the government).
Victims are asked to provide a bank account into which the money can be transferred and promised a large percentage of the money for performing the service. In same cases, victims may also be asked to pay a fee or a series of fees for the release of the money.
Once the victim has provided account information, the criminals will often drain their bank accounts, and occasionally use that information to open new, fraudulent accounts.