In recent weeks many newcomers to the Internet have exchanged warnings of a computer virus called Penpals. According to rapidly spreading legend, if you receive and try to read an e-mail of that title, an embedded program will take over your machine, causing your processor to fuse and wiping your hard disk clean.
But the fact is that there is no such virus - and never could be. Instead, Penpals is an example of a "meme" - a virus of the mind, spread by people discussing it. It "lives" by being repeated to more people. And one of the most effective is one which preys on people's fears.
In the past couple of years other memes - including Irina and, most notorious of all, Good Times - have also caused havoc on the Net, not by damaging machines but by tying their users' minds into anxious knots.
The idea of a virus of the mind was first put forward by Richard Dawkins in 1975. "I didn't know about computer viruses when I wrote about memes," he said last week. "But the Internet is an appropriate laboratory for watching them in action."
Ian Whalley, editor of Virus Bulletin magazine, by which virus hunters stay in touch, says that the reason why people are worried is that more have a connection to the Internet, but only understand the technology peripherally. "PCs are becoming more like TVs, in that you can plug them in and they work, and you can be surfing the Net in no time," he says. "If you got somebody ringing you up and telling you not to watch a particular programme on the TV because it would explode, you wouldn't believe them. But if it's 'The Internet', people believe most things."
There are still plenty of genuine computer viruses out there, although anti-virus software can catch most of them - such as Michelangelo, which is due to strike this Thursday, 6 March. Any infected computer could have its hard disk erased - for real.