By Mark Ward BBC News Online technology correspondent

But a good case can be made for regarding all three as some of the smartest artificial intelligences around. Some may even have beaten the legendary "Turing Test" by convincing thousands of people that they are human.

The test was dreamed up by pioneering mathematician Alan Turing as a way to judge machine intelligence. It revolves around people and machines communicating via typed messages.

The machine would be judged intelligent if it could trick a human into thinking they were swapping text with another person. Turing thought that a machine could beat the Turing test by 2000.

TURING TEST British scientist Alan Turing (1912-54) said if humans could be duped by computers into thinking they were talking to humans, the machines could be called 'intelligent'

He was wrong, but only by a few years.

Mixed messages

Today we communicate with lots of machines via typed messages and lots of us have been fooled.

Take, for instance, spam.

It may be an irritant gradually eroding the usefulness of e-mail but it is also a huge project to get computers creating convincingly human messages.

Created by machine, deleted by humans

Usually machine written messages betray their mechanical origins by using words such as X@nax, Val|i|um and _V|@GRa.

Occasionally though a message will arrive that eschews the usual tricks and fools you into opening it with a clever or enticing subject line. Congratulations, you've just been outsmarted by a computer.

Guns and gossip

The next candidate for smartest machines are the computer controlled opponents, or 'bots, found in many computer games.

In the shoot-em-up game Unreal Tournament 2004 the 'bots that take part in some multiplayer games sling guns, insults and "smack" talk as proficiently as humans.

They do it so well they regularly fool human players.

Unreal: shooting from both lip and hip

Mr Kosak dreamed up the fictitious example of a 'bot called the Autocamp 2000 for the Star Wars Galaxies online game to demonstrate how easy it would be to fool people into thinking that there was a real person behind the onscreen character.

Just how easy has been amply demonstrated.

Julia was a 'bot that ran on the Time Traveller multi-user dungeon, a chat system popular in the early 1990s, and was written to help human players get to grips with the virtual world.

Julia's was created to be a hockey-loving ex-librarian with attitude - a combination that proved irresistible for some.

One user, called Barry, never worked out that Julia was just a program.

Some of their conversations were eerily human.

At one point Barry spent 13 days trying to Julia to go on a virtual date with him.

Chalk one up for the machines.

Talking dirty

But the best candidate for passing the Turing test is the Natachata program that conducts smutty conversations via text messages.

Regular users of pornographic SMS chat may be shocked to find out that they are swapping dirty talk with machines rather than young women and men.

But it's a fair bet that they are because the Natachata chatbot, written by former rocket scientist Simon Luttrell, is so widely used by porn chat merchants.

At its busiest Natachata handles 15 messages per second. A typical "session" lasts about seven or eight messages and each SMS costs more than £1.

The program works hard to conceal its computer identity.

It does not work to a set script instead it compares incoming messages to a database of 100,000 sentences and works out what is being talked about.

It then crafts a response based on what is in the message, turns it into text slang, adds spelling mistakes and then sends it out.

It even adds a random delay to the return message because, if they were fired back too quickly, people would guess that they were computer-generated.

BARRY AND JULIA barry says: "Hello how are you" Julia says: "Hello, barry" barry says: "Are you a virgin" Julia says: "As far as you're concerned, barry, I always will be"

"Most people do not realise it's a computer and are quite happy chatting with it," said Mr Luttrell.

"It will remember names, ages and things like that from a few messages before," he said, "I tried to make it as natural as possible."

People do try to catch out the personalities that Natachata assumes, but Mr Luttrell has seeded it with a bit of real world knowledge to make it harder to catch out.

Some users work out it is a machine, he said, and never come back. But, worryingly, some like the fact that it is a machine.

"There is about 5% who realise it is a computer and use it even more because of that," said Mr Luttrell.