WHEN MALICIOUS PROGRAMS started spreading havoc through the computer world, security experts were quick to spot the similarity with disease and dub the invaders "viruses". The analogy is apt. Computer viruses carry the information they need to replicate. They need the resources of a host to survive and can wreak havoc on whatever they infect. And having replicated, they exploit their host to spread to others.

The computer industry has been remarkably slow in taking the analogy to its logical conclusion—that to protect themselves from attack, computers need an immune system. But now US researchers have taken that step. Using immunology as their guide, they have developed security systems for computers that automatically detect and respond to an intruder, even if it's one they've never seen before. And the methods don't just work for viruses, they'll repel hackers too.

Computer viruses invade their hosts by hiding in files, programs or ...