Now, the letters spelling out the sentence you are reading represent the tiniest fraction of the information hurtling around the internet.

Millions of e-mails are swapped daily. The number of documents posted on the World Wide Web grows by a million a day and is estimated to reach eight billion by 2002. And more than £330bn will be spent online in the next two years.

More than 200 million people around the world now log on and the net has become the fastest-growing communication tool ever invented.

The prototype e-mail was sent three decades ago by Professor Leonard Kleinrock, credited by many as the father of the internet. He managed to get his computer at the University of California in Los Angeles to talk to another computer at a separate research centre at Stanford, near San Francisco.

Helen Briggs, of BBC Science: "The internet is now the fastest-growing communication tool ever invented."

Moments after the two letter message was sent, the computer crashed.

"All we wanted to do is log on to their machine from mine. And to log on you have to type L-O-G," said Professor Kleinrock.

"And so my guy typed the L, and we said: 'Did you get the L?' And the message came back: 'Got the L.' He typed the O. 'Did you get the O?' 'Got the O.' Typed the G. 'Did you get the G?' Crash! The machine failed.

"So the first message on the internet was 'LO'? Or 'Hello', crash!"

The network that grew out of this first internet message was soon up and running.

It was known as ARPAnet, after the US Government agency which funded it, the Advanced Research Projects Agency. The agency was set up by the US defence department following the launch of the Soviet Union's Sputnik satellite.

The scientists behind ARPA wanted a robust system for electronic communications.

Some experts dispute whether ARPAnet was really the birth of the internet. A rival date is 2 September, when Prof Kleinrock and his team succeeded in hooking up their computer to a switch.

"So at that time you had a computer talking to a switch for the very first time, and without that you could not have computer talking to computer," he said.

But one group of enthusiasts have decided to adopt 20 October as the day the internet was born, and have created an electronic birthday card that can be signed by anyone. The card forms part of their "Internet Day" website.