More than 100 countries are believed to be using the Internet for espionage, says McAfee, the information technology security company, in a report released on Thursday.
"This is the rough consensus of the security experts we have spoken to, and a credible figure given how low the barriers to entry are. All you need is a few computer science graduates," said Ian Brown, lead researcher for McAfee and a security expert at Oxford University.
The report finds that the number of cyber-espionage incidents and computer attacks on critical national infrastructure are rapidly increasing around the world.
This year had seen a record number of incidents in which countries reported an attempt to infiltrate their defence information systems or an attack aimed at disrupting key organisations such as air-traffic control, financial services or utility companies.
"There are signs that intelligence agencies around the world are constantly probing other governments' networks, looking for strengths and weaknesses and developing new ways to gather intelligence," Peter Summer, an information systems expert at the London School of Economics, says in the report.
One of the highest-profile incidents was in April, when Estonian officials accused Russia of mounting a series of cyber-attacks that brought down the websites and information technology networks of state institutions such as the president's office, ministries, parliament and the police, as well as political parties.
News organisations and banks were also targeted.
"The sequence of events [in Estonia] looked a lot like the sort of thing a government would do in order to check how much it could get away with.
"The whole thing bears the hallmark of a 'false flag' operation. We've seen terrorists carry out such 'defence probes' ahead of physical attacks," said Yael Sahar, at Israel's International Institute for Counter-Terrorism.
In July, a US Pentagon computer was hacked into, with officials suggesting that the attack came from the Chinese military. Germany's chancellery computer systems were reported to have been attacked by Chinese hackers. China has strongly denied any involvement in these incidents but it has previously said that it is pursuing activities in cyberespionage.
There have been attacks reported on government computers in Australia, New Zealand and India.
"This is the first year we have seen governments stand up and accuse other gov-ernments of hacking their systems," Mr Brown said. "It is a sign of the increasing severity of the problem."
The cyber-espionage incidents are likely to accelerate government spending on computer security.
The US air force, for example, said in September that it was planning to create a command focused on preparing for war in cyberspace.
Copyright The Financial Times Limited 2007.