ST. LOUIS -- A discovery by two Washington University scientists in the mid-1990s could play a role in preventing the kind of credit card fraud that recently affected customers of the suburban St. Louis-based grocery store chain Schnucks.

The St. Louis Post-Dispatch reported that Marcel Muller and Ron Indeck were attempting to shrink bits of data when they learned that magnetic media have what amounts to a fingerprint.

Tiny signals are present on the magnetic medium that comprises both hard drives and the stripes on the back of credit cards. If the unique "fingerprint" on those stripes is compared to the so-called fingerprints in a database, fraud can be detected.

"It's a tiny signal, and most credit card readers consider it noise, and they filter it out," said Robert Morley, an associate professor of electrical and systems engineering, who worked with the two scientists. "But we amplify the data, so we can pull that signal out and identify the card."

California-based MagTek has adopted the technology, seeding the market with millions of card readers that can detect the fingerprints.

"The easiest analogy is a human fingerprint," said Mimi Hart, the company's chief executive. "Your fingerprint has a lot of minutiae points on it. But when you put your finger down, depending on how you roll it or the pressure you put on it, the sensor is going to pick up different minutiae points."

When a swipe yields something that correlates closely enough to the fingerprint in the database, the system can tell the original card is being used. But if the swipe reveals a print that's identical to the fingerprint in the database, the system will know it's a clone.

"We know, statistically, we're always going to get a different value, but one that's highly correlated," Hart said. "When we get two that are identical, we know that's statistically impossible."

Now, Hart said, the technology just needs to be "turned on" and used.

Schnucks Markets Inc. last month said it was the victim of hackers who somehow gained access to credit card and debit card information of customers. The chain is working with police, attorneys general in Missouri and Illinois, the U.S. Secret Service and the FBI.

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Information from: St. Louis Post-Dispatch, http://www.stltoday.com