London has begun a two-day international conference focused on the threat from cyber-security attacks.
Representatives of 60 nations gathered to discuss how to tackle the rising levels of cyber-crime.
Foreign Secretary William Hague convened the London Conference on Cyberspace, and urged a "global co-ordinated response" on policy.
However, Wikipedia founder, Jimmy Wales, warned that ill-advised interventions posed their own risks.
The event came a day after intelligence agency GCHQ warned that cyberattacks on the UK were at "disturbing" levels.
Experts attending the conference included EU digital supremo Neelie Kroes, Cisco's vice-president Brad Boston and Joanna Shields, a senior executive at Facebook.
US Secretary of State Hillary Clinton had been due to attend, but cancelled the trip on Monday night after her 92-year-old mother fell ill.
Mr Hague led the opening session.
"We want to widen the pool of nations and cyberusers that agree with us about the need for norms of behaviour, and who want to seek a future cyberspace based on opportunity, freedom, innovation, human rights and partnership, between government, civil society and the private sector," he said.
However Mr Wales, who also took part in the first event, urged caution.
"The biggest threat to the internet is not cybercriminals, but misguided or overreaching government policy," he said.
Speaking later in the day, Prime Minister David Cameron appeared to agree that politicians should resist the temptation to be heavy-handed.
"Governments must not use cyber security as an excuse for censorship," he said.
Mrs Clinton's speech was delivered by US vice president Joe Biden. He also warned against the dangers of a "repressive global code".
"What citizens do online should not, as some have suggested, be decreed solely by groups of governments making decisions for them somewhere on high," he said via a video-link address from Washington.
'Very real threat'
On Monday, Baroness Neville-Jones, the prime minister's special representative to business on cybersecurity, said Russia and China - who are both attending the conference - were some of the worst culprits involved in cyber-attacks.
And Iain Lobban, the head of GCHQ, warned that a "significant" attempt was made to target the computer systems of the Foreign Office and other government departments over the summer.
Some reports at the time quoted intelligence sources as saying China was responsible for that attack.
With cybercrime estimated to cost £600bn a year worldwide, Mr Lobban, writing in the Times ahead of the summit, warned that the "disturbing" levels of illegal activity online represented "a very real threat to our prosperity".
Britain said it wanted to develop a set of international "rules of the road", establishing "norms of acceptable behaviour" in cyberspace, while stopping short of a full treaty advocated by some countries.
Mr Hague said a "collective endeavour" was needed to tap into the "enormous potential" of cyberspace.
"How to ensure we can all reap the benefits of a safe and secure cyberspace for generations to come is one of the greatest challenges we face," said Mr Hague.
"The response does not lie in the hands of any one government or country but it is too important to be left to chance. This needs to be a collective endeavour, involving all those who have a stake in cyberspace.
"The ideas and proposals we hope to emerge from the conference will develop into the 'London Agenda' - an inclusive and focused approach to help us realise the enormous potential cyberspace offers for a more prosperous, safe and open networked world."
The government has put aside £650m of additional funding to help tackle computer-based threats over the next four years, Mr Hague added.
'Drain the swamp'
Ross Anderson, professor of security engineering at Cambridge University, said there had been a "great growth" in cybercrime over the past six years.
As many as 5% of PCs are infected with malware - short for malicious software - Prof Anderson said, and there was a one in 20 risk that any given computer was sending spam without the owner's knowledge.
"If you want to defend against this kind of threat it's not enough to just shoot a few crocodiles, you have to drain the swamp," Prof Anderson told BBC Radio 4's Today programme.
"We need action against the whole ecology of cybercrime, not purely defensive measures to protect, for example, the Foreign Office."
Misha Glenny, author of Dark Market, which looks at the issue of cybercrime, said those involved were not, on the whole, engaged in traditional organised criminal activities.
But he added: "We're seeing a migration of traditional organised crime groups over into cyber, exploiting a new type of person engaged in crime who tends to be young, technically sufficient, very good at maths and physics, but perhaps not your traditional criminal figure in the outside world."