A group of cyber experts stunned a conference when they showed the vulnerability of GSM mobile networks which can be easily exploited by hackers enabling them to impersonate a user's identity and make calls from his account without a clue to the consumer.

The ethical group -- matrix shell -- gave a demonstration of the hacker's technique on a live network of a leading mobile service provider in which they managed to make a call using the number of a audience member without actually using his phone or SIM.

Explaining the weaknesses of the GSM service providers at Nullcon, a conference of cyber security experts, defence and intelligence officials and ethical hackers, the group claimed that most of the telecom networks were not encrypting signals, which is common at the international level.

Akib, one of the group members, said another issue is authentication of a user by a mobile network when call is made.

However, Director General of Cellular Operators Association of India Rajan Mathews said, "this is not unusual and can happen to any operator. The networks of operators are handled by third party who are global players (like IBM, NSN).

Operators have methods and protocols in place to detect any such intrusion into their networks."

He also said whenever such a thing happens, the customer also calls to bring it to notice. So, operators are equipped to handle such situations.

Explaining the technique, he said just like every mobile phone has a unique identity number, called as IMEI number, the SIM cards have a unique identification number called as IMSI and in order to hide the identity of the user, the networks camouflage IMSI with a temporary identification number TMSI.