By Tim Weber
Business editor, BBC News website, Davos
Criminals controlling millions of personal computers are threatening the internet's future, experts have warned.
Do you know if your PC has been taken over by cyber-criminals?
Up to a quarter of computers on the net may be used by cyber criminals in so-called botnets, said Vint Cerf, one of the fathers of the internet.
Technology writer John Markoff said: "It's as bad as you can imagine, it puts the whole internet at risk."
The panel of leading experts was discussing the future of the internet at the World Economic Forum in Davos.
Mr Cerf, who is one of the co-developers of the TCP/IP standard that underlies all internet traffic and now works for Google, likened the spread of botnets to a "pandemic".
Of the 600 million computers currently on the internet, between 100 and 150 million were already part of these botnets, Mr Cerf said.
Botnets are made up of large numbers of computers that malicious hackers have brought under their control after infecting them with so-called Trojan virus programs.
While most owners are oblivious to the infection, the networks of tens of thousands of computers are used to launch spam e-mail campaigns, denial-of-service attacks or online fraud schemes.
Mr Markoff, who writes for the New York Times, said that a single botnet at one point used up about 15% of Yahoo's search capacity.
It used retrieved random text snippets to camouflage messages so that its spam e-mail could get past spam filters.
"Despite all that, the net is still working, which is amazing. It's pretty resilient," said Mr Cerf.
The expert panel, among them Michael Dell, founder of Dell computers, and Hamadoun Toure, secretary general of the International Telecommunication Union, agreed that a solution had to be found to ensure the survival of the web.
But its members were unsure about feasible solutions, even though they identified operating systems and authentication as key issues.
Microsoft has tried to toughen up its programs' security measures
It was still too easy for net criminals to hide their tracks, several panel members said, although they acknowledged that it was probably not desirable that every individual was definitively identifiable.
"Anonymity has its value, and it has its risk," said Jonathan Zittrain, professor for internet governance at the University of Oxford.
Operating systems like Microsoft Windows, meanwhile, still made it too easy for criminals to infiltrate them, the experts said.
Microsoft had done a good job improving security for its latest operating system, Windows Vista, said Mr Markoff.
But already pirated copies of Vista were circulating in China, even though the consumer launch of Vista has been scheduled for next Tuesday.
Experience showed that about 50% of all pirated Windows programs came with Trojans pre-installed on them, Mr Markoff said.
Mr Dell said the future might bring "disposable virtual PCs", accessed through the internet, that would minimise the threat of a persistent virus infection.
Mr Toure said that whatever the solution, the fight against botnets was a "war" that could only be won if all parties - regulators, governments, telecoms firms, computer users and hardware and software makers - worked together.