Nato countries’ defence ministers met last week to finalise the organisation’s first policy covering cyber attacks on member states’ critical national infrastructure.

After hacking campaigns against Estonia in May, and Whitehall and the Pentagon in October, the profile of electronic warfare is on the rise.

Computer-based spying and the hacking of military systems have been a staple of conflicts since the Cold War. But the attacks are getting bigger and more organised, tilting at the age-old counter-espionage target of destabilising a country from afar.

Estonia was subjected to a systematic campaign to bring it to its knees following removal of a Soviet war memorial, according to Mihkel Tammet, director of communications and IT at the country’s Ministry of Defence.

“These attacks were not aimed at ruining our databases or stealing our information. They were assaults on the service industry and our nation’s infrastructure,” said Tammet.

And they were co-ordinated and well-funded, he said.

First the attackers tested the bandwidth of Estonia’s ISPs. Then, over a period of three weeks, deluges of spam disrupted government systems, news portals and banking sites.

Assaults on the financial sector were particularly effective. The two main banks, representing three-quarters of the industry, saw their online services disabled for almost 24 hours.

“Estonia is 97 per cent dependent on internet banking and cash is not common, so many people had serious problems,” said Tammet.

The disruption of news web sites maximised the psychological impact by making it hard for people to find out what was going on.

Critically, the situation cannot be blamed on Estonia’s poor cyber defences. The government has good links with industries and ISPs, and was prepared for the attacks.

“Few countries would have been as good as Estonia at keeping networks running for those three weeks,” said Anil Suleyman, head of Nato’s Computer Incident Response Capability, speaking in a personal capacity.

The developed world has a lot to learn from Estonia’s experience, not least because future attacks may be more severe thanks to the increasing use of botnets - ­ networked groups of infected computers that generate vast quantities of spam.

Cyber attacks will be a key part of future conflicts. And the potential for using computers as a first-strike weapon is also not being ignored, according to James Lewis, director of the Center for Strategic and International Studies think tank.

“There are perhaps 20 nations developing these skills to gain military advantage,” said Lewis.

“In warfare these tactics could be far more serious. Nations will need to be able to defend themselves against a sustained cyber campaign.”