A stressed e-mail from a friend once read: "A worm has just eaten my kid!"

Thankfully, the message was not referring to infanticidal earthworms, but rather to a type of computer virus, a "worm", that had just infected some files (known as KID files) on his computer.

And he may have had Fred Cohen to thank for the ensuing implosion of his computer hard-drive.

Mr Cohen released the very first computer virus in a controlled experiment in a class at the University of Southern California, 25 years ago today.

In 1983, in a class at the School of Engineering taught by the computer-programming guru Leonard Adleman, Mr Cohen wrote a program for a parasitic application that seized control of computer operations.

Though he later went on to pioneer and develop computer virus software and defence systems, Mr Cohen also demonstrated in 1987 that there is no computer algorithm that can be written to detect and perfectly identify all computer viruses.

Hence the despair of computer users around the world whose PCs have ground to a halt due to any one of the thousands of viruses, from Trojan horses to lops and worms.

Spam e-mails promising nude photos of alluring celebrities tempt lascivious surfers to click on links to infected pages, downloads spiked with malicious software stalk your hard-drive to monitor your internet use, personal details and passwords are hoovered up by stealthy undervcover viruses, and programs cease to function as they are consumed from within by mysterious parasitic infections.

Mr Cohen continues to work for major companies, consulting on virus defence systems and information protection, but neither he nor any other viral policeman can stop the spectral hackers from having their fun at the expense of our long-suffering hard drives. Our only option is to batten down the anti-virus hatches and hope for the best.

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