Common sense says that you should lock your doors and windows to prevent thieves from entering your house. The advice is no different when dealing with digital crooks.

According to the FBI's Crime Complaint Center, computer users logged more than 270,000 cases of potential Internet-based fraud during 2006, resulting in $198.4 million in losses -- or $724 per complaint.

Sadly, few of these schemes were particularly sophisticated. Nigerian email fraud, for example, had the highest median loss, at $5,100. That's why fellow Fool Bill Mann has said that if it's from Nigeria, hit delete.

But suspiciously polite Nigerians have nothing on auction fraudsters, to whom the FBI attributed 44.9% of complaints. Auction fraud, as it turns out, is not unlike what the sub-Saharan scammers proffer. Although auction buyers and sellers routinely have to deal with problem transactions, this kind of fraud has nothing to do with your own auctions. Instead, you get an email saying that either:

  • Someone needs to contact you about something you're buying or selling
  • You still owe money for something you bought via auction, or
  • You're owed money for something you sold via auction.

When you respond to the email's request for financial info, BAM! The identity thief has you.

On balance, these tricks work more often than other schemes because auctions managed by companies like eBay (NASDAQ:EBAY), (NASDAQ:AMZN), and Overstock (NASDAQ:OSTK) have become very big business. Digital auctions also require easy ways to transfer money online -- PayPal, for example.

Still, there's good news here. These thieves are only able to take money from the terminally stupid. Too harsh an assessment, you say? Perhaps, but all of this fraud could have been prevented with two simple steps:

  1. Have a good junk email filter.
  2. Don't respond to junk messages from people you don't know.

Or, in simpler terms, lock the windows and doors on your computer. Digital thieves, like the real kind, have just one interest: separating you from your money. Don't let them.

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Fool contributor Tim Beyers writes about personal finance weekly. Have a Foolish money tip? Tell him.

Tim didn't own shares in any of the companies mentioned in this article at the time of publication. Amazon and eBay are Stock Advisor picks. Overstock is a former Rule Breakers selection. The Motley Fool's disclosure policy thinks digital thieves should pack sunglasses and a bathing suit for the afterlife. It'll be pretty warm where they're headed.