An Israeli scientist said his team had found a way to break into mobile phone calls made on the popular GSM network, allowing eavesdroppers to listen in on calls and even take on a caller's identity.

The GSM Association, representing vendors who sell the world's largest mobile system, which is used by more than 860 million consumers in 197 countries, confirmed the security hole but said it would be expensive and complicated to exploit.

Professor Eli Biham of the Technion Institute in Haifa said he was shocked when doctoral student Elad Barkan told him he had found a fundamental error in the GSM (Global System for Mobile communications) code.

"I told him (Barkan) that it was impossible," Biham told Reuters. "I said such a basic mistake would already have been noticed by someone else. But he was right, the mistake was there."

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