Computer insecurity: Citibank ATM scam shows that PINs are vulnerable to hackers

SAN JOSE, Calif. — Hackers broke into Citibank's network of ATMs inside 7-Eleven stores this year and stole customers' PIN codes, according to recent court filings that revealed a disturbing security hole in the most sensitive part of a banking record.

The scam netted the alleged identity thieves millions of dollars. But more importantly for consumers, it indicates criminals were able to access PINs — the numeric passwords that theoretically are among the most closely guarded elements of banking transactions — by attacking the back-end computers responsible for approving the cash withdrawals.

The case against three people in U.S. District Court for the Southern District of New York highlights a significant problem.

Hackers are targeting the ATM system's infrastructure, which is increasingly built on Microsoft Corp.'s Windows operating system and allows machines to be remotely diagnosed and repaired over the Internet. And despite industry standards that call for protecting PINs with strong encryption — which means encoding them to cloak them to outsiders — some ATM operators apparently aren't properly doing that. The PINs seem to be leaking while in transit between the automated teller machines and the computers that process the transactions.

"PINs were supposed be sacrosanct — what this shows is that PINs aren't always encrypted like they're supposed to be," said Avivah Litan, a security analyst with the Gartner research firm. "The banks need much better fraud-detection systems and much better authentication."

It's unclear how many Citibank customers were affected by the breach, which extended at least from October 2007 to March of this year. The bank has nearly 5,700 Citibank-branded ATMs inside 7-Eleven Inc. stores throughout the United States, but it doesn't own or operate any of them.

That responsibility falls on two companies: Houston-based Cardtronics Inc., which owns all the machines but only operates some, and Fiserv Inc., based in Brookfield, Wis., which operates the others.

A critical issue in the investigation is how the hackers infiltrated the system, a question that still hasn't been answered publicly.

All that's known is they broke into the ATM network through a server at a third-party processor, which means they probably didn't have to touch the ATMs at all to pull off the heist.