"There is a cyberwar going on," Hamadoun Touré, secretary general of the International Telecommunication Union, said during a cybersecurity debate at the Geneva Press Club.
"Just like a conventional war, there are no winners, only destruction," he warned an audience of reporters, diplomats and technology experts.
While Touré declined to pin the blame on individual countries, such attacks have become common currency.
Russia was widely blamed for what has been dubbed the world's first cyberwar, in 2007, when state and bank websites were blocked for days in Estonia, one of the world's most wired nations and a member of NATO and the European Union.
Since then, attention has focussed on China for alleged state-run cyber attacks on targets in the United States and elsewhere.
In recent weeks, pro-regime Syrian hackers and North and South Korean online warriors have also made headlines.
In an increasingly connected and Internet-dependent world, cyber attacks by governments and criminal gangs alike have the potential to wreak havoc on everything from the financial sector to key public services, Touré said.
That raises the spectre of huge economic losses and social chaos, and Touré said governments and business worldwide must think collectively about how to head that off.
"No one single entity can do it alone," he said.
"We have to change the mindset."
Touré questioned whether nations and businesses were "mentally prepared to work with one another".
He said, "In this arena, there's no such thing as a superpower anymore" because it is cheap to create viruses and launch attacks.
"It's the human brain that's driving this," Touré said.
"So we're all equal in this, and we need to come together," he said.
"That's the new order — it's not one country.
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"It's not like a nuclear power, where the technology, the knowledge base and the infrastructure and the funding are required for that.
"We have to treat cyberspace like we treat the real world."