A trio of computer students and professionals could not resist the challenge: proving "tamperproof" digital cellular phones are actually vulnerable.

After about six hours of work, two graduate students at the University of California at Berkeley and a computer cryptologist were able to "clone" the phone, allowing them to make unauthorized calls from another phone."Given the state of the security of other cellular phone systems, I wasn't terribly, terribly surprised," said Ian Goldberg, one of the students. The three looked at the project as a challenge.

USA Today reported the breakthrough on Monday.

Still, the amount of time and effort it took to clone the codes makes the digital phone security much more difficult to circumvent than analog cellular phones, which in comparison are easily breached.