Nato is treating the threat of cyber warfare as seriously as the risk of a missile strike, according to a senior official.

A London conference was told that online espionage and internet-based terrorism now represent some of the gravest threats to global security.

Suleyman Anil, who is in charge of protecting Nato against computer attacks, said: "Cyber defence is now mentioned at the highest level along with missile defence and energy security.

"We have seen more of these attacks and we don't think this problem will disappear soon. Unless globally supported measures are taken, it can become a global problem."

Anil, who is head of Nato's computer incident response centre, told the E-Crime congress in London that the cost of hi-tech strikes on government communications was falling, while the amount of damage they could inflict grew.

Among the chief threats is cyber terrorism, in which attempts are made to shut down online communication networks or use the internet to attack official institutions. Although some have warned of the possible threat since the 1980s, it is only in recent years that the issue has made it onto the radar of governments around the world.

But Anil also warned of rogue nations who could sponsor internet-based attacks on Nato members. "There are nations who are not just working on defence capabilities, but who have attack capabilities - and that brings a new dimension to the whole issue," he said.

The annual E-Crime congress is one the largest gatherings of those who work to combat cyber crime. Delegates included banking experts, police and IT industry luminaries, all keen to discover new ways to fight online crime.

The prospect of internet-based warfare has come to the fore after a series of high-profile international attacks. Last year, it emerged that a gang of hackers, believed to be from China, had infiltrated computer systems at the Pentagon and launched attacks on government networks in Britain, Germany, India and Australia. US officials, who have labelled the group Titan Rain, have accused them of operating under the auspices of officials in Beijing.

Another strike in Estonia, which has one of the most hi-tech governments in the world, was initially blamed on hackers backed by the Russian authorities. However only one teenager, an Estonian, has been arrested in connection with the incident so far.

To coincide with the congress, shadow home secretary David Davis will today announce Conservative proposals on online crime - including the creation of a new post of cyber security minister. The Tory plans also outline the reinstitution of a national hi-tech crimes police squad, and forming a dedicated unit inside the Crown Prosecution Service for dealing with computer crime cases.

"Cybercrime is a growing and serious threat to individuals, business and government. It is a problem that will continue to escalate as technology changes," said Davis.

Kevin Poulsen, a former hacker who is now an editor with technology magazine Wired, has accused politicians and the media of overplaying the fear factor.

"In some ways, Estonia's attacks were less sophisticated than previous 'cyberwars' - like those between Israeli and Palestinian hackers, India and Pakistan, China and the US," he said. "Even those attacks fell short of a cyber war, at least as experts have defined the term. I'm sceptical that real cyber war, or cyber terrorism, will ever take place."

Despite the lack of hard evidence on the nature or identities of cyber terrorists, however, the threat is deemed serious enough for the White House to allocate $6bn (£3bn) for strengthening its systems against attack.

Those plans have been characterised by critics as a potential invasion of civil liberties. Bush administration officials say they are a necessary defensive measure. Homeland security secretary Michael Chertoff has called it "one area where we have significant work to do".