The Best Buy cash registers used a Wi-Fi network, which uses a standard known as 802.11b. It runs on three channels in the unregulated 2.4GHZ spectrum, which is also used by cordless phones, microwave ovens and many Bluetooth products. Because the information is transmitted through the air, a person can "capture" the information from the parking lot outside the store or anywhere within about 300 feet of the source.
Harris said the store is investigating whether a security breach occurred. She declined to comment on when the machines might be put back in service or whether Best Buy has called in law enforcement officials.
Wireless networks are notoriously insecure, but they have spread to at least 30 million homes and businesses worldwide.
Hackers say it would be tough, but not impossible, to use this open door to ride the network all the way into a company's main computer.
"Plugging them into your network is like dangling your network out the window," said David Black, security technologies manager at management consultants Accenture.
The wireless cash registers are portable and were only used when the lines got too long at the stores' standard registers, which plug directly into each store's central computer, Harris said.
"These registers are not Best Buy's main register terminals and (they) represent a small percentage of transactions," Harris said.
Discuss: Best Buy bans wireless registers
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