The other scam in the Nigerian 419 scam.
Here you get a letter or e-mail from a person in Nigeria (or wherever) saying that for all sorts of reasons they have 40 million pounds in the bank that nobody knows about (a rich relative died or it was profits from a dodgy oil deal etc).
They are trying to get it out of the country and looking for someone abroad who will store the money in their account.
Once they get out the country they will come and claim their money, and give you 10% (or whatever) for your troubles.
All they need is your bank details so they can deposit this 40 million pounds.
Of course if you agree you never see a penny of this 40 million pounds, and you find your bank acount emptied.
This scam can be extended by asking you to pay a small amount for "administration", if you fall for this they then want a bit more for "tax", then if you fall for this they want a bit more because the deal is getting complex. You either keep paying or give up when you realise you are being conned.
It always amazes me people fall for this.
Why did they chose you (they do not even know you), also would your bank not notice 40 million going into your account and ask questions, and also why should you trust them when they admit they are trying to steal all this money.
But every year idiots fall for it, see here
http://home.rica.net/alphae/419coal/