Three undersea cables carrying vital web traffic were cut within four days last week, and no one yet knows why

One of the most intriguing internet mysteries of recent times - which has puzzled conspiracy theorists and experts alike - deepened today when experts said they were still no closer to establishing why a cable under the Mediterranean broke last week, causing a serious disruption to the world's internet traffic.

Today a ship moved into position off the coast of Egypt and began repair work on the cable. It was one of three undersea cables between Europe and Asia to be damaged in the space of four days last week, causing networks to collapse in Egypt, Kuwait, and as far away as India.

Early reports suggested that a ship which had been forced to drop its anchor in heavy seas accidentally snapped the cable, which is buried only half a metre beneath the ocean floor, but a spokesman for the company which runs it said today it could be a week until the cause is known.

The cable, which is only the width of a finger, snapped at a point 8km off the coast of Alexandria early on Wednesday morning, forcing network operators in Egypt and nearby countries to re-route traffic. Within two and a half hours another cable - understood to be close by - also broke.

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Between them, the two cables - which stretch tens of thousands of kilometres - carry as much as 70 per cent of the internet traffic between Europe and Asia. Operators suddenly found themselves having to re-route traffic that would usually travel along cables through the Suez and out across the Indian Ocean across the Atlantic.

Then at 5:59am on Friday a third cable 59km off the coast of Dubai, in the Persian Gulf, also broke - apparently in an unrelated incident - affecting traffic in the United Arab Emirates. Usually, the only reason a number of cables in an area may break simultaneously is an earthquake, but there was no evidence of one in either area last week.

It is thought that the first two cables were broken after a severe weather warning in the Mediterranean Sea forced weather officials in Egypt to tell ships in the vicinity of Alexandria to drop their anchors. Two of the 40 ships that were nearby are thought to have unwittingly dropped their anchors on top of the cables, and severed them.

A source close to Flag Telecom, which runs the cable, said today: "Everyone is saying it was a ship's anchor, but the truth is, it's all speculation. We don't know yet why this happened."

Conspiracy theories, meanwhile, have proliferated, blaming the cuts on everyone from the US Government to Al Qaeda. One report on a telecommunications website referred to the maxim of Goldfinger, the James Bond villain: "Once is happenstance, twice is coincidence, the third time is enemy action."

Adding to the confusion is the fact that the Egyptian Government has said that no ships were in the area at the time the cable was damaged, suggesting that an anchor was not the cause.

In a statement, the Egyptian Ministry of Communications said: "A marine transport committee investigated the traffic of ships in the area, 12 hours before and after the malfunction, to figure out the possibility of being cut by a passing vessel and found out there were no passing ships at that time.

The Ministry added that the site was "a restricted area, which excludes the possibility that the malfunction resulted from a crossing ship."

Security experts said today that it was unlikely a terrorist group had sought to interrupt the global communications network - firstly because such groups rely on the internet for their operations, and secondly because they would be unlikely to possess the necessary diving equipment.

"They'd be shooting themselves in the foot," Alex Schmid, director for the Centre for the Study of Terrorism and Political Violence, said. "Plus, these cables are buried in the seabed hundreds of yards beneath the surface of the ocean, and are difficult to reach. There are endless vulnerabilities in infrastructure, but these have to be weighed against the size of the threat, and the risk involved."

Two of the cables are run by Flag Telecom, which is owned by the Indian telecommunications giant Reliance. A spokesman for Flag Telecom said today that repair work had begun on both cables and that service had been restored to affected customers via alternative routes.

The company that runs the third cable could not be reached for comment.

Accordingly to Renesys, a company which monitors the web's performance globally, the severance of the cables has "greatly impacted" phone and internet services to the Middle East.

The worst affected areas were Kuwait, where one internet service provider lost its network entirely, and Egypt and Pakistan, where several lost more than 70 per cent of their coverage, according to reports.

A spokesman for BT described the impact on internet users in Britain as "minimal".

Paolo Rosa, a spokesman for the International Telecommunications Union, said that submarine cables were prone to being affected by earthquakes, fishing equiment, and anchors, but that in high-risk areas, particularly near coastlines, they often split in two so that traffic could be re-routed in the event of damage.

A spokesman for the UK Cable Protection Committee, which negotiates with the fishing industry on behalf of British telcos, said that often cables were snapped by the beams that boats use to keep their fishing nets open, and which frequently drag along the seabed.