419 scams or advance fee frauds have been around for hundreds of years. They normally involve someone making contact with you by various means
( with the internet becoming the most used medium ) and striking up a relationship. Then two things could happen :

1. A romantic relationship could develop, and after a period of time the 'target' wants to meet the other person. The other person agrees to come to the 'targets' country for a meeting, promising everything. Then just days before the person is due to fly to the 'target' they suddenly lose their air ticket or money.

The 'target' is notified. A naive person, hoping for a relationship, is encouraged to send money to the person overseas.

After the money is sent they never hear from the person again.

2. Another form of  scam is where the 'target' is offered a huge sum of money. out of the blue, from a person stating they need it out of their country asap. They offer the 'target' money to accept the transfer of the funds and assist in the movement of the money.

Then, when the 'target' agrees and the transaction is supposedly ready to go, the fraudster suddenly needs money to facilitate the transfer. They state they cannot use the funds they want to transfer because they cannot withdraw them. The target anticipating a huge windfall sends money......... need i say more.

There are many variations to this - beware !! I have tried to keep it simple !! The people behind these things come from many countries in the world, so take care out there