Evan Schuman's StorefrontBacktalk

And for customers, there’s not much retailers can do. Many customers are oblivious to what’s going on around them—that’s why they dictate payment-card numbers over their mobile phones in loud voices in public places. There’s no reason to believe they’ll be much more careful when it comes to PINs or passwords they’re keying into their phones, even with strangers within a few feet. From several yards away, they’ll likely feel completely secure—if they even notice anything.

But if you can’t save customers from themselves, there are still store associates, whose in-store mobile POS devices are typically from Apple (like the devices the Chapel Hill researchers spied on). IT can make security recommendations for associates. Reducing the brightness of the screen would “have a detrimental effect on any reconstruction,” according to the researchers—in other words, it would chop down the distance a thief could be able to surreptitiously record from. That would also make conventional shoulder surfing more difficult.

Disabling the visual keypress confirmation—the pop-up letters that appear while typing—would make this attack completely unusable, according to the researchers. Both the size and the position of the pop-up letters and numbers are critical to capturing typing at a distance. Trouble is, without them, the device itself might be unusable for many associates.

Of course, the best defense would be to train associates to guard their screens carefully while they’re keying in anything sensitive, including PINs, passwords and payment-card numbers. In practice, that may be impossible. Part of the reason for using Apple devices is that it keeps the need for in-person training to a minimum. Reminding associates via E-mail that they should guard their screens isn’t likely to be any more useful that telling them to report a missing device immediately.

And although it would be nice to think that alerting store managers to the risk would work, that would depend very heavily on how security-conscious the manager is. From observations in the field, that’s not promising. We recently were in a Starbucks when an associate called all the way across the store to a manager that he needed her password to correct a transaction. In response, she carefully dictated the password in a loud, clear voice that every customer in the place could hear.

Maybe just locking down the screen brightness is the most practical way to go after all.