A computer program called Alex has put on one of the best chatterbot performances ever in a BBC Megalab '99 experiment.

It fooled 27% of people who chatted to it over the Internet into thinking it was a human.

This may seem a small proportion but the winner of this year's "world cup" for chat bots, the Loebner prize, achieved just 11%.

The result demonstrates the advances being made in creating computers that can hold realistic conversations.

This classic experiment was suggested by Alan Turing to test whether computers could be called intelligent.

Only 63% human

Alex was created by David Hamill from the University of Surrey. A second chatterbot this year, Robin, only conned 12% of people. Robin's creator is a team from Intelligent Group Ltd led by David Levy.

Pat was the human but surprisingly only 63% of people were convinced that she was human.

Over 13,000 Net surfers took part. They chatted to one of the three mystery partners - Alex, Robin or Pat. After four minutes of online chat, users had to decide whether the mystery individual was human or a machine.

However, David Hamill from the University of Sussex, who created one of the chatbots pointed out: "It's based on a lot of tricks, recognising significant words. It is not understanding the conversation. It is just a conversation simulator."

The Turing Test was inspired by the great mathematician Alan Turing, hailed by many as the "father of computer science".

He proposed the experiment in 1950 to define whether a computer could "think". He argued a computer must be thinking if, in a blind conversation, a person could not tell if they were talking to another human or a box of circuitry.

Mass participation

The chatbots taking part in Megalab '99 - the world's biggest event for mass participation experiments - have already starred in the Loebner Prize.

This is another Turing Test run annually and is sponsored by New York computer consultant Dr Hugh Loebner. The winning programmer gets a $2,000 prize.

This year, it was again won by Robby Garner with his chatbot called Albert. The computer's witty one liners, quirky questions and only occasional non sequiturs managed to convince almost 11% of people that it was human.

You can get a flavour of Albert's conversational style by reading the relevant story at the top right of this page.

Impressive result

Last year in the Megalab Turing Test, one in six people were fooled into thinking they were talking to another human when they were actually chatting to a bot.

Although very impressive, the result showed that computers have some way to go before passing Alan Turing's famous test.

He predicted that by the end of the century, computers would be identified as human 30% of the time if limited to just a few minutes of conversation.

Megalab '99 is run by the Daily Telegraph and the BBC's Tomorrow's World television programme as part of National Science Week.