"We don't yet know how best to protect ourselves against infrastructure breakdowns," said Eric Domage, a senior executive with the information technology consultancy group IDC.

The Internet, which emerged at the start of the 1990s, is a vast global information network linking numerous sub-networks which use the same communication language, the IP or Internet Protocol, enabling different computers to communicate with each other.

This vast linkage rests on an infrastructure spanning the world: routers, datacentres, servers and billions of small re-routers that can direct traffic into various networks via terrestrial and submarine cables or by satellite.

Among the weakest points of the Internet are the so-called backbones, the main arteries forming a "vertebral column" for the network interconnecting all the sub-networks and continents.

In Asia, a large share of the traffic which could not transit the damaged submarine cables was nevertheless re-routed as an emergency measure to servers in the United States.

But Eric Domage warned of the danger of becoming totally dependent on the United States.

He says the only solution would be to develop major electronic backup systems, in other words reinforced infrastructure such as submarine cables or routers, plus other links including by satellite.

Today, 50 percent of world traffic transits via one US state, Virginia, where most maritime terminals arrive and where the bases of most of the main root router centres are to be found which can transform an address in letters into an IP address.

The root routers are particularly sensitive. "A hacker or a power cut can put them out of service and the Internet user then does not have access to sites," explained Romain Levy, a specialist with the information technology laboratory Lexsi.

And there are in fact only very few in the whole world, mainly in the United States, Britain and Sweden, notes Emmanuel Sartorius, a senior defence official at the French economics ministry.

One country is therefore technically in a position to "disconnect" another.

The effects of line disruption as happened in Asia can be contained if links can be transferred to wireless technology, by satellite or Wimax (wireless broadband), say sources at France Telecom.

The other danger is that of attacks by Internet pirates.

"A hacker can take control of a DNS router and put it out of action," said Paulo Pinto, head of the infotech security research laboratory Sysdream. In the absence of an alternative line, "if the emergency backup does not work, a hacker can disconnect a continent".

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