The biggest ever is =N= 2 Billion scam performed by Anajemba, Nwude et al. They duped a Brazillian Bank

. I think they wanted the bank to fund a contract for building the Abuja International airport.
We have advance yahoo boom now though. So many student are into it. I have witnessed the stuff happen. Its called advanced yahoo because they use 'jazz' on the foreigners. I witness 4 friends who all cashed between =N=11M - 18M within a week last month from their victims.
The biggest scams however are outside Nigeria. So many corporate frauds out there