Internet chaos was caused by one boy
By Nic Fleming and Kate Connolly in Berlin
A self-confessed computer vandal arrested in May was responsible for 70 per cent of all viruses received worldwide in the first half of this year.
Sven Jaschan, 18, was still at school in Germany when he admitted writing and spreading the Sasser and Netsky "worms" and their variations, which caused vast irritation and damage.
Graham Cluley, senior technical consultant at the computer security company Sophos, said: "It is simply staggering that a single German teenager can have had such a dramatic impact."
The Sasser worm caused huge disruption to businesses and organisations in May, hitting, among others, British Airways, the Maritime and Coastguard Agency, Taiwan's national post office, government departments in Hong Kong and Australia's Railcorp train company.
The Sophos report also shows that many more new viruses are being created. The company detected 4,677 new types of virus up to the end of June, up 21 per cent on last year. Actual numbers of infections are not known because many remain unreported.
However, of all e-mails sent, around one in 11 contain viruses.
Police arrested Jaschan at his family home in Waffensen near Bremen on May 7 after being tipped off by individuals motivated by a $250,000 reward that was offered by Microsoft for information leading to conviction.
A court date has not yet been set. Technically he could face up to five years in prison, but he may escape a custodial sentence because he wrote the viruses before his 18th birthday in April.
Jaschan told the German magazine Stern that he spread the viruses to gain his peers' respect and admiration. "I felt as if I had written a first-class essay. How Netsky spread, I think it's terrific, and my classmates thought I was terrific.
"Then it was reported on TV. That was cool. Only occasionally did I wake up in the middle of the night and think, yikes, there might be trouble."
He is now hoping to turn from poacher to gamekeeper by seeking a job with a computer security company.