The sums involved are usually in the millions of dollars, and the investor is promised a large share, typically ten to forty percent, in return for assisting the fraudster to retrieve or expatriate the money.

In that con, businessmen were contacted by an individual allegedly trying to smuggle someone connected to a wealthy family out of a prison in Spain.

In exchange for assistance, the scammer promised to share money with the victim in exchange for a small amount of money to bribe prison guards.

The scam has been used with fax and traditional mail, and is now prevalent in online communications like emails.

The number "419" refers to the section of the Nigerian Criminal Code dealing with fraud, the charges and penalties for offenders.

Some victims even believe they can cheat the other party, and walk away with all the money instead of just the percentage they were promised.

The essential fact in all advance-fee fraud operations is the promised money transfer to the victim never happens, because the money does not exist.

An email subject line may say something like "From the desk of barrister [Name]", "Your assistance is needed", and so on.

The details vary, but the usual story is that a person, often a government or bank employee, knows of a large amount of unclaimed money or gold which he cannot access directly, usually because he has no right to it.

For example, in 2006, 61% of Internet criminals were traced to locations in the United States, while 16% were traced to the United Kingdom and 6% to locations in Nigeria.

One reason Nigeria may have been singled out is the apparently comical, almost ludicrous nature of the promise of West African riches from a Nigerian prince.

If a victim makes the payment, the fraudster either invents a series of further fees for the victim, or simply disappears.