You've likely received more than one of these emails. Someone in "Nigeria" is looking to deposit, donate, or otherwise move a fortune to the U.S.--and wants to pay you a hefty commission for helping.

Of course, you clicked "delete," and probably said to yourself, "These guys need to get a better story."

But the "Nigerian letter" emails must work occasionally, or you wouldn't still be receiving them. How can they possibly be effective? Researchers at Microsoft have studied that very question, and are now reporting that the fraudster's preposterous prose is backed by solid business logic that underscores three important principles of effective advertising.

1. Target Buyers, Not Just People

Imagine for a moment that you're a online fraudster. You send out millions of emails, but can't afford to waste time with someone who won't eventually fall for your scam. What's the best strategy? You can craft a cleverly worded plea and get thousands of responses. Or, you can scrawl a message with bad grammar, a third-world tie-in, and ridiculous claims of instant wealth that only the most gullible and uninformed will fall for.

Sounds crazy, right? But, of course, those are exactly the people you're looking to find.

Entrepreneurs face a similar problem: how to target only serious customers without wasting advertising dollars on people who aren't likely to buy. The higher your sales costs, the more important the question becomes. A online store owner might not be too concerned that most of the ad clicks to his website are unproductive. On the other hand, a face-to-face sales effort is much more costly and therefore requires a much higher closing ratio to be profitable.

As is true for the scammers, your advertising dollars are most effective when used to filter for likely buyers rather than just attracting the masses.

2. Prequalify Your 'Customers'

Once the bogus email has landed in the inbox of one of the half-dozen people in the western hemisphere that have never heard of the Nigerian scam, the outlandish story also pre-qualifies the potential victim in another key area--their willingness to "buy" the scheme.

Fraudsters need victims whose desire for wealth--whether greed or need--will overwhelm their common sense. The scammer's promise of huge wealth is designed to hook folks willing to toss caution to the wind.

Your goals aren't so different, if you think about it. Legitimate businesses want to know if a potential customer has the resources to buy, and when he or she is likely to make a decision. You don't want to expend sales resources chasing potential customers who may not actually be in the market for your products. A well-crafted advertising campaign will help your company prequalify customers based on need, budget, and timeline.

3. Disqualify the Time Wasters

For the Nigerian scammer, turning away the wrong person is probably as important as finding the right one. That's why the scammer doubles down on the poor grammar and outrageous claims--he's just making sure that you and I have absolutely no interest in responding.

Successful businesses prequalify customers in the same way. That's why high-end advertisers often include prices in advertising--such as the Jaguar ad stating that leases start at "only $649 a month." They aren't trying to impress you, but rather to disqualify customers who can't actually afford the car.

Properly targeted advertising limits time and frustration of people who aren't appropriate for your product or service--and keeps your sales team talking only to likely buyers.

How'd the fraudsters figure out all of this? The Microsoft report speculates that the scammers have fine-tuned their approach by trial and error.

But after all the people they've taken advantage of, it's only fair that the rest of us can finally get some benefit.