But Krebs obtained a copy of an information sheet prepared by the Department's Crime/Intel Analysis Unit that says Nordstrom located a total of six skimming devices attached to registers.
The alert outlined what was seen on the the retailer's surveillance footage. The thieves, all men, worked in teams of three. Two men distracted the sales staff while a third took pictures of the register, then removed its rear access panel and took additional photos.
Several hours later, three different men entered the store. Again, two of them distracted the sales staff while the third removed the register's back panel and installed the skimmer. The police memo described the device:
It captures all track data from credit card transactions and stores it on the device, similar to a USB drive. The connector was made to match the connections on the back of the register to include color match. Therefore, no one would have detected it unless there was a problem with the register.
It's unlikely customer card information was compromised in this case, as the devices were discovered before the crooks could retrieve them and download the information they had recorded. But for as little as $135 they could have purchased keystroke loggers capable of sending the stolen information over a local wireless network.
Victor Searcy, director of the Fraud Resolution Center at IDentity Theft 911, said he wasn't surprised the bad guys have found "yet another nefarious method" for stealing consumers' personal information.
"This scheme, involving smaller, harder-to-detect skimming devices, puts the onus on businesses to heighten their security efforts," Searcy said.
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Many retailers have card readers that connect to cash registers via PS/2 connections. These are now vulnerable to this kind of skimming attack and need to be secured.
The bottom line
We all need to be aware of the potential for this sort of identity theft. It can happen no matter how hard you try to protect yourself. So you need to remain vigilant.
That's why it's so important to continually review all the transactions on your credit card and bank account statements. If you spot charges that aren't yours, report them right away. And if you're at a store and see someone tampering with a register, say something to a store employee.
—By CNBC contributor Herb Weisbaum. Follow him on Facebook and Twitter
@TheConsumerman or visit The ConsumerMan website.