Sven Jaschan has confessed to writing the Sasser and Netsky worms, and was arrested following a tip-off to Microsoft
A report published by Sophos, a world leader in protecting businesses against viruses and spam, has revealed that 70% of virus activity in the first half of 2004 can be linked to a German teenager.

Just two of Jaschan's viruses, the infamous Sasser worm and Netsky-P, account for almost 50% of all virus activity seen by Sophos up until the end of June. Counting Jaschan's other released variants of the Netsky worm, the total figure accounts for over 70%.

"For a single German teenager to have such an impact on computer security is simply staggering," said Graham Cluley, senior technology consultant for Sophos. "If one of Jaschan's friends had not informed Microsoft about his identity then the situation may have been even worse."

Jaschan was arrested at his home in the sleepy village of Waffensen, North Germany in early May after a tip-off to Microsoft, but his virus continue to infect computer users and have an impact.

"It's like Pandora's box - once released viruses can carry on spreading even if the author has been caught or realises he has done something wrong," explained Graham Cluley. "However, because Jaschan was under 18 at the time he released the viruses it's possible he will escape a stiff sentence if found guilty."

The Sasser worm hit home computer users and companies worldwide, including the South African government, Taiwan's national post office, and the UK's coastguard service.

Sophos believes that it is possible that some of Jaschan's fellow college students may still be charged in connection with assisting him in the writing and distribution of the viruses.