The basic idea behind the scam was that an extremely wealthy person in Nigeria had his accounts frozen or could not transfer money out of the country without help. The scammer either requested that money be sent or that bank account numbers be sent to facilitate the transfer of the scammer's assets for which the person would be rewarded handsomely later.
That this was a scam seems obvious, as why would some wealthy African need the assistance of random Americans? However, everyone knows about the scam because it worked. The scammer just needs one person out of millions to take the bait. That is true with most common scams. Only one person needs to take the bait to make attempting to scam thousands worth the scammer's time.
Another old scam is still making the rounds, according to the Wichita Eagle, in "A long-lost relative left you money? Beware of inheritance scams."
In this scam, the intended victim is told that a relative has left them an inheritance, but to get the inheritance, the victim must first pay the scammer money to facilitate the transfer. Often this scam can be very personal, as the victim is given the name of a real relative who died or lived in a faraway place as the person who left the inheritance. That makes the scam sound plausible.
The best way to protect against this scam is to know it exists, and if you receive anything that looks like it, to check with other relatives before sending any money to claim the inheritance.
Still not convinced that the scam is a phony? Contact an estate planning attorney to check it out for you.
Reference: Wichita Eagle (August 21, 2015) "A long-lost relative left you money? Beware of inheritance scams"