At this point, disenfranchised "Nigerian royalty" asking for money through a poorly worded email is the ultimate cliche of internet scams.

So why does it still exist?

According to new book "Think Like A Freak," a follow-up to the popular "Freakonomics" by Steven D. Levitt and Stephen J. Dubner, the scam's obviousness is its chief selling point.

The book refers to research from Microsoft Research computer scientist Cormac Herley, who looked at Nigerian scams — technically called advance-fee fraud — from the point of view of the scammer. How, he wondered, were scammers who never sent an email free of typos earning enough money for the United States Secret Service to establish its own task force to fight them?

In fact, those typos are a key part of the scam.

Levitt and Dubner explain the genius behind such an obvious scam in terms of "false positives," referring to email recipients who engage with the scammers but don't ultimately pay. Reaching out to scores of potential victims isn't much work, thanks to the ease of email, but with each reply from a gullible target, the scammers are required to put forth a little more effort.

Therefore, it's in the scammers' best interest to minimize the number of false positives who cost them effort but never send them cash. By sending an initial email that's obvious in its shortcomings, the scammers are isolating the most gullible targets. If you trash their email, that's fine. They don't want you, someone from whom there's virtually no chance of receiving any money. They want people who, faced with a ridiculous email, still don't recognize its illegitimacy.

As Herley tells the book's authors, "Anybody who doesn't fall off their chair laughing is exactly who they want to talk to."

While no one is recommending you engage with scammers, Herley tells Levitt and Dubner that the best defense against these crooks is to game their system and waste their time. Ideally, he says, this would take the form of a chatbot that engages with scammers, to make them put in the effort toward the false positives they're trying to avoid.