Nigeria is probably the best-known African country where advance-fee-fraud scams originate. Indeed, the scams are known as 419 scams, after section 419 of the Nigerian penal code, which prohibits the crime.

"It's generally accepted that the 419 scams originated in Nigeria, and there is a growing perception that the miscreants involved have now started relocating to neighboring countries," said Steve Santorelli, director of Global Outreach at Team Cymru, an Internet security research firm.

Last year, Nigeria's Economic and Financial Crimes Commission (EFCC) instituted a ban on nighttime Web browsing in public places, conducted raids on cybercafés in Lagos and other cities, and succeeded in making some highly publicized arrests, but the problem has not been fully stamped out.

"Cybercafés are fertile ground for this type of scam; once a keystroke logger is installed on a café computer, the machine becomes a harvester of login information for every other person who uses it; it's one reason I advise travelers to carry a netbook or smartphone, rather than using a public machine," added Limbelabs' Zimmerman.

In one of the latest scams, criminals take over e-mail accounts and send messages to contacts, saying the person is stuck in Nigeria after being robbed and needs money to sort hotel bills. The e-mail then gives an alternative e-mail address where the contact can send money via Western Union or any other form of instant transfer.