Spanish authorities are reported to have arrested 310 people as part of an international investigation into one of the Internet's most active "419" or "Nigerian e-mail" fraud rings.

The raid, carried out in conjunction with the FBI, saw police enter 166 properties across southern Spain, confiscating 2,000 mobile phones, 327 computers, and 165 fax machines, and seizing over 200,000 euros in cash. The fraudsters appear to have been monitored by international police authorities for two years.

The large-scale fraud is said to have involved a number of different cons, including lottery frauds and classic e-mail scams where respondents were promised a fee for acting as a conduit for funds. The group sent out millions of unsolicited e-mails as a way of hooking gullible respondents, though they appear to have diversified into old-fashioned letter scams as well.

It is believed to have had as many as 20,000 victims in 45 countries ranging from the U.K. and U.S. to Japan and Australia, netting the criminals tens of millions of euros, possibly more. The arrests are said to have been mostly of Nigerian nationals, though details have not been confirmed.

The scale of the operation is unprecedented, and underlines the highly organised and extensive nature of the modern e-criminal ring. Given the number of arrests and the volume of material to plough through, it is likely to take time for the full extent of the fraud to be determined.