Mobile devices are essentially computers operating through a network – and, because that network is public, they are much more vulnerable than their desktop and laptop counterparts.

A criminal who wants to listen to your conversations or steal your data has several ways to do it: he can infect your mobile device with a Trojan horse or other malware disguised as an SMS message or web-page – or install a physical hijack module costing less than USD 100.

He can intercept your calls using a portable base station – impersonating the network and using its protocols to force your device to communicate in low-security mode. Even 3G devices, with their higher encryption standards, are vulnerable to such an attack.

Or he can use the human factor, relying on a corrupt law enforcement or telephone company employee to intercept your communications within the network – where it is not encrypted.

All three approaches are technically feasible and increasingly cheap. And the worst is, they are invisible: you would never know if they are being used on you.