Someone has noticed that the Starbucks' iPhone application can be copied with a screen grab from a neglected handset, enabling the thief to gorge themselves on free coffee*.

The payment system relies on reading a bar code from the iPhone's screen, identifying the customer and debiting their account. But the barcode doesn't change – and the iPhone has a screen-grabbing function built in, so leaving your handset on the table could allow anyone nearby to make an instant copy of your details and even mail them straight to themselves right from the phone.

Kelley Langford, of System Innovators, based in Florida, reckons he can do that in 20 seconds, and has demonstrated the process repeatedly – showing people just how insecure the Starbucks application is, and presumably drinking a lot of free coffee while doing so.

Most on-screen barcode systems, such as those used for train tickets in the UK, are single-use codes that only work once. But the Starbucks system uses a static code to identify the customer, on the basis that minimal security is necessary to protect the value the user has loaded into the account to pay for coffee, but one might imagine that even low-value transactions need some protecting.

NFC-based payment systems obviously can't be copied in this way, but even on-screen bar codes can be made more secure with the addition of simple transaction counter, or time stamp, but it seems Starbucks eschewed either option for the sake of simplicity.

The coffee thief still needs access to victim's iPhone, if only for a few seconds, to run the app and grab the screen. So more likely to attract practical jokers than organised criminals, but a good example of how badly a payment system can be designed if one puts one's mind to it. ®

Bootnote

* Sometimes Starbucks puts tiny amounts of this in its brown-tinged milk.