An 18-year-old German schoolboy was responsible for 70 per cent of all viruses affecting businesses and homes in the first half of 2004.

And according to a report from security software firm Sophos, the number of new viruses being written is on the increase with 1,157 detected during July - the highest figure since December 2001.

Sven Jaschan, who was still at school near Bremen when he was arrested in May, this week openly admitted to creating the Sasser and Netsky worms, which hit a huge number of UK organisations, including the UK coastguard.

Jaschan was tracked down after a tip off, which came after Microsoft announced a $250,000 bounty for information leading to conviction.

Businesses are facing the threat of increasingly sophisticated and changing viruses from virus writers and organised crime syndicates, with new technologies such as wireless and smartphones being targeted.

'Wireless connectivity such as 802.11b and Bluetooth is on the increase and the bad guys are going to look at this as a target,' said David Emm, senior technology consultant at security firm Kaspersky Lab.

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