Organisers of a new "419" style e-mail scam are trying to extort money by pretending to be involved in the fight against fraud.
The self-styled "Anti-Scam Crusaders" lured victims using a genuine South African-based anti-fraud website.
This latest scam attempts to solicit money for the publication of a book with instructions on how to beat scams.
Named after a Nigerian anti-fraud law, 419ers typically use mass e-mails to trick people into parting with money.
The writer of the e-mail claims to have "understudied the Nigerian 419 actors", who "have been able to get some morally weak citizens of other countries to collaborate with them".
The e-mail pretends to be promoting a book that "contains all it would take to knock the 419ers out of business".
Then comes the catch: "However, a little premium will be required from you, if you are interested to obtain the manuscript for publication in your country."
The fraudsters registered on the 419 Legal website, a genuine anti-fraud initiative, and used the site's private message facility to contact other subscribers.
"They approached our website last year offering help with tracing offenders in Nigeria," Inspector Rian Visser, the founder of 419 Legal, told the BBC News website.
"We then launched an investigation, found they were involved in fraud and banned them from our website."
But in March this year the fraudsters reappeared, operating from a different server in Nigeria and registering new bogus user identities.
Inspector Visser, an officer in the South African Police Services (SAPS), started 419 Legal last year on his own initiative.
"We wanted to close down the communications networks of these criminals," Inspector Visser said.
"We decided we would inform the internet service providers and tell them we could provide all the proof that was needed."
Inspector Visser said 419 Legal now had the backing of the SAPS and benefits from a network of 5,000 informers around the world. The organisation works in co-operation with investigating authorities in Nigeria, the UK, the US and Australia, among others.