A computer security researcher has built a device for just USD 1,500 that can intercept some kinds of cell phone calls and record everything that's said.

The attack Chris Paget showed yesterday illustrates weaknesses in GSM, one of the world's most widely used cellular communications technologies.

His attack was benign; he showed how he could intercept a few dozen calls made by fellow hackers in the audience for his talk at the DefCon conference here.

But it illustrates that criminals could do the same thing for malicious purposes, and that consumers have few options for protecting themselves.

Paget said he hopes his research helps spur adoption of newer communications standards that are more secure.

"GSM is broken _ it's just plain broken," he said. GSM is considered 2G, or "second generation," cellular technology.

Phones that run on the newer 3G and 4G standards aren't vulnerable to his attack.

If you're using an iPhone or other smart phone and the screen shows that your call is going over a 3G network, for example, you are protected.

BlackBerry phones apply encryption to calls that foil the attack, Paget pointed out.

But if you're using a type of phone that doesn't specify which type of network it uses, those phones are often vulnerable, Paget said.

Paget's device tricks nearby cell phones into believing it is a legitimate cell phone tower and routing their calls through it.