By Spencer Dalziel

A US HACKER has used open source software to break mobile phone networks and listen in on conversations.

Occasional freelance security expert and hacker Chris Paget built the system for less than $1,000. That was spent on the hardware required to break GSM phones. The rest of his hack used only open source software that is of course freely available to anyone with an Internet connection.

According to Reuters, US coppers spend a fortune on expensive snooping kit called IMSI catcher. Now Paget is offering to demo his much less expensive alternative at Defcon after the Black Hat convention.

Paget's hack so far only works using GSM technology but that is used by big US telcos like AT&T and T-Mobile.

A probably self-satisfied Paget told Reuters that "GMS is broken" and "it's really not hard to build these things."

There's no mention of which opens source software was used to break GSM. However, only a few days ago an open source GSM cracking tool was released called Kraken.

GSM encryption was first cracked at the tail end of 2009 and now a hacker has released more open source GSM hacking tools.

Apparently, AT&T declined to comment while the T-Mobile didn't respond to any calls. That must be because the companies have booked front row tickets for Paget's presentation at Defon and will be furiously taking notes.