A stolen credit card is an obvious threat to a consumer's identity, since a string of fraudulent purchases can swiftly undo someone's good credit standing. But most identity-related fraud occurs outside the credit system, according to a recent survey by IdentityHawk, a company that sells identity protection services.

The company found that 17% of American consumers have been victims of ID theft, and 28% of all households have at least one member who's been hit by the crime.

Credit card account fraud was the most common type of identity theft, comprising 20% of all cases, IdentityHawk found. But what about the other 80%? The second most-common identity theft scenario involves the sale of personally identifiable information, including Social Security numbers. Theft of bank account debit cards came in third, affecting 16% of ID theft victims.

The reason why any of this matters is that most systems to detect and stop identity theft rely on observing credit transactions, often by looking for anomalies in purchasing history. If a teacher in Kansas suddenly uses his credit card to buy 30 laptops in Hong Kong, for example, that might prompt Visa to raise a red flag and investigate whether the purchase is legit.

That's a potential problem, says Jeff Paradise, IdentityHawk's executive director, since institutions and consumers may need to be looking elsewhere to detect when identities have been stolen.

"Eighty percent of all losses related to identity theft happen outside the credit system---and the earliest detection that an identity might be compromised occur with a breach like a false address," Paradise said in a press release.

[Tool: Quickly assess your risk of identity theft for free]

Image: Son of Groucho, via Flickr.com