The surveillance of around 100 phones, including the prime minister's, was done through spy software installed in the central system of Vodafone, the mobile telephony provider serving those targeted, the government explained yesterday.

Government spokesman Theodoros Roussopoulos said the tapping functioned through 14 mobile phones, which were geared to activate when people made or received calls on the targeted cell phones.

An investigation showed that Vodafone antennas in the central Athens areas of Lycabettus, Mavilis Square and the Athens Tower were used in the eavesdropping operation.

«The investigation discovered a special code in the software which permitted cell phone interception,» said Justice Minister Anastassis Papaligouras.

The process may have continued had Ericsson not evaluated Vodafone's equipment during a check.

Indeed, people with the right equipment can easily intercept phone calls, telecommunication experts told Kathimerini.

It takes just a second to tap a phone call, since mobile phone networks (GSM) have major security flaws which can be manipulated, the experts added.

Mobile phone companies can protect themselves from such tapping - which is illegal - by updating their equipment, though such upgrades are expensive.

«Companies must make changes to systems at base stations and replace the chips in all mobile phones - a procedure which is very expensive,» said Costas Papadatos, manager at security adviser Encode.

In an effort to reduce mobile phone tapping in the future, Nikos Alexandridis, who is the president of the National Post and Telecommunications Center (EETT), recommended the establishment of an anti-hacker task force, which could intervene when phone calls are intercepted.