Six men from Nigeria and Benin were convicted of fraud by a Dutch court and will receive prison sentences of between 301 days and four and a half years.
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Two of the men, including the suspected leader of the group, also have to return €205,702 (£147,550) each to one of their victims.
The six were accused of sending thousands of e-mail messages, faxes and letters to people all over the world, making up various stories to lure people to Amsterdam, from where they operated. The victims were told that their help was needed to transfer money or that they had won a lottery.
The "419 Fraud" or "Advance Fee Fraud", have been around since the early 1980s, but it is only in the past few years that the fraudsters turned to the internet.
The senders of the e-mail messages often purport to be family members of a former African dictator in need of help to funnel money out of the country. In return for the help, they promise between 10% and 25% of the fortune.
A Russian man was lured into paying thousands of dollars after the fraudsters told him he had won an internet lottery. Not only did he pay a "transfer fee", but also fees for a "non-drugs statement" that was required, according to the West-African con men.
The victim only discovered that he had been scammed after he was told to pay $35,000 (£21,497) for a "non-terrorism statement".
A Swiss professor gave the scammers $482,000 (£296,000) after he was told he would receive $9m (£5.5m) for his help with laundering millions of dollars. The Swiss man paid for chemicals that the scammers said were necessary for "cleaning" the bank notes, according to the charges.
The Swiss professor, however, helped the Dutch police by luring five of the six fraudsters to a train station in Amsterdam, where they were arrested in the summer of 2002. The sixth man was arrested a few months later.
Dutch police estimated that the scammers made millions of euros.
Maarten Rejnders writes for WebWereld Netherlands