The German man who supplied the firepower for last week's attacks on major commercial websites says he did it for the good of the Internet.

The 20-year-old from the Hanover area would only be identified as 'Mixter'. He said in an e-mail interview that he posted the devastating software and instructions on the Web four months ago.

He denounced the use of his Tribal Flood Network package by unidentified hackers to attack at least seven major sites as 'stupid and pointless'. He said his motive was to aid security standards on the Internet.

But Internet security chiefs denounced him as a 'bomb-maker' who had 'thrown a loaded gun into a room crowded with kids'.

The FBI was last night continuing its hunt for those who planted Tribal Flood Network programs on hundreds of host 'zombie' computers, timed to flood the targets with messages.

These are know as 'denial of service' attacks since they cause the target to crash under the volume of incoming traffic. They do not compromise data such as credit card details.

The identity of the hackers, probably an organised group, who launched the attacks is unknown although a theory was that they were protesting against increasing political and commercial control of the Web, and the fortunes being made in Internet stocks. FBI investigators and computer security experts traced the attack to two universities in California, a location in Oregon and one in Germany.

A desktop computer at the University of California in Santa Barbara was used for Tuesday's attack on CNN while while on-line trader eBay was hit in part from an Internet router at Stanford University. In neither case were the university authorities aware of the use to which the equipment had been put.