This week's onslaught of the Sasser computer worm underlined fears that digital weapons may become the latest addition to the arsenal of global terrorism. Computer networks are obvious targets for terrorists because so much of modern life depends on them. Beyond the impact on banks and businesses around the world, in Britain, the Sasser worm brought down the computerised mapping system at the Coastguard Agency and, in Australia, disrupted communications between train drivers and signal boxes, leaving 300,000 passengers stranded.

Security services everywhere have been aware of the threat of cyberterrorism for some time. Britain's Terrorism Act of 2000 refers to attempts to "disrupt an electronic system", and the website of MI5 includes a warning about electronic forms of attack. However, to judge from the ease with which worms such as Sasser continue to spread, such warnings are not being heeded.