Image credits: Keystone/getty images; right: richard harrington/three lions/getty images Punjab photo/afp/getty images; Nuclear power corp. of India; T.C. Malhotra/getty Images Babu/Reuters; SONDEEP SHANKAR/ Bloomberg News/Landov; B Mathur/Reuters

Click here for a full-sized version of this timeline

While this is the first major infiltration to involve cellphones, the scheme did not depend on the wireless nature of the network. Basically, the hackers broke into a telephone network and subverted its built-in wiretapping features for their own purposes. That could have been done with any phone account, not just cellular ones. Nevertheless, there are some elements of the Vodafone Greece system that were unique and crucial to the way the crime was pulled off.

We still don't know who committed this crime. A big reason is that the UK-based Vodafone Group, one of the largest cellular providers in the world, bobbled its handling of some key log files. It also reflexively removed the rogue software, instead of letting it continue to run, tipping off the perpetrators that their intrusion had been detected and giving them a chance to run for cover. The company was fined €76 million this past December.

To piece together this story, we have pored through hundreds of pages of depositions, taken by the Greek parliamentary committee investigating the affair, obtained through a freedom of information request filed with the Greek Parliament. We also read through hundreds of pages of documentation and other records, supplemented by publicly available information and interviews with independent experts and sources associated with the case. What emerges are the technical details, if not the motivation, of a devilishly clever and complicated computer infiltration.

The cellphone bugging began sometime during the fevered run-up to the August 2004 Olympic Games in Athens. It remained undetected until 24 January 2005, when one of Vodafone's telephone switches generated a sequence of error messages indicating that text messages originating from another cellphone operator had gone undelivered. The switch is a computer-controlled component of a phone network that connects two telephone lines to complete a telephone call. To diagnose the failures, which seemed highly unusual but reasonably innocuous at the time, Vodafone contacted the maker of the switches, the Swedish telecommunications equipment manufacturer Ericsson.

We now know that the illegally implanted software, which was eventually found in a total of four of Vodafone's Greek switches, created parallel streams of digitized voice for the tapped phone calls. One stream was the ordinary one, between the two calling parties. The other stream, an exact copy, was directed to other cellphones, allowing the tappers to listen in on the conversations on the cellphones, and probably also to record them. The software also routed location and other information about those phone calls to these shadow handsets via automated text messages.

Five weeks after the first messaging failures, on 4 March 2005, Ericsson alerted Vodafone that unauthorized software had been installed in two of Vodafone's central offices. Three days later, Vodafone technicians isolated the rogue code. The next day, 8 March, the CEO of Vodafone Greece, Giorgos Koronias, ordered technicians to remove the software.

Then events took a deadly turn. On 9 March, Tsalikidis, who was to be married in three months, was found hanged in his apartment. No one knows whether his apparent suicide was related to the case, but many observers have speculated that it was.

The day after Tsalikidis's body was discovered, CEO Koronias met with the director of the Greek prime minister's political office. Yiannis Angelou, and the minister of public order, Giorgos Voulgarakis. Koronias told them that rogue software used the lawful wiretapping mechanisms of Vodafone's digital switches to tap about 100 phones and handed over a list of bugged numbers. Besides the prime minister and his wife, phones belonging to the ministers of national defense, foreign affairs, and justice, the mayor of Athens, and the Greek European Union commissioner were all compromised. Others belonged to members of civil rights organizations, peace activists, and antiglobalization groups; senior staff at the ministries of National Defense, Public Order, Merchant Marine, and Foreign Affairs; the New Democracy ruling party; the Hellenic Navy general staff; and a Greek-American employee at the United States Embassy in Athens.

Within weeks of the initial discovery of the tapping scheme, Greek government and independent authorities launched five different investigations aimed at answering three main questions: Who was responsible for the bugging? Was Tsalikidis's death related to the scandal? And how did the perpetrators pull off this audacious scheme?

To understand how someone could secretly listen to the conversations of Greece's most senior officials, we have to look at the infrastructure that makes it possible.

First, consider how a phone call, yours or a prime minister's, gets completed. Long before you dial a number on your handset, your cellphone has been communicating with nearby cellular base stations. One of those stations, usually the nearest, has agreed to be the intermediary between your phone and the network as a whole. Your telephone handset converts your words into a stream of digital data that is sent to a transceiver at the base station.