It is thought that "spimmers" have developed the idea because of the attention-grabbing nature of IM, and the increasingly effective spam filters that specialist companies have developed.

Research firm the Radicati Group estimates that 582 billion instant messages were sent in 2003.

The US-based technology analysts expect the amount of spim sent to increase to 1.2 billion messages this year, up from 400 million in 2003.


Just talk
Most people use IM to talk quickly and informally to friends and colleagues.

So there are fears that some people may be taken in by the spim messages because they think they are being directed to certain websites by people they know.

In fact, the messages are generated automatically, in a very similar way to spam.

Once the program is written and run, all the spimmer has to do is wait and see if anybody responds.

It is a very low maintenance method of sending out junk messages as the system is automated.

Even if a tiny fraction of people fall for the spim, it can be a very lucrative business.

However spim itself it not particularly dangerous on its own, according to Alyn Hockey, technical director at internet security firm Clearswift.

In an interview with Radio Five Live's Up All Night he played down the threat of spam via IM.

"It's not really as dangerous as spam," he said. "With spim, it tends to be more of an annoyance."

This, he says is because IM protects you from the immediacy of, for instance, a pornographic e-mail which could portray an offensive image immediately upon being opened.

"With instant messaging, if I wanted to send you a piece of pornography, I'd have to send it as an attachment for you to download and open."

This requirement to download any attachments offers a degree of protection. That is also why spim is not a credible threat when it comes to viruses either.


Simple advice
It is hoped that messaging services will act before spim spirals out of control.

"There are products being created to help control this," said Mr Hockey.

"The manufacturers will have improved the software to eradicate it before it really becomes an epidemic."

For now, people using IM should be wary and follow some simple advice.

"Don't accept connections from people you don't know, don't download attachments from people you don't know; and keep your anti-virus software and operating system up-to-date," said Mr Hockey.