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The spread of the latest e-mail virus, Sircam, highlights the cat-and-mouse game being played out between virus writers and their prey.

In the middle are IT departments and companies offering sophisticated systems to detect and remove computer worms ready to invade computer hard disks and distribute their venom.

So why would anyone open a file which says "look at this joke, it's really funny," or "seen this latest picture of Anna Kournikova?", given that there has been so much publicity about the respective viruses.

MORE STORIES 'Personal' Sircam virus targets Europe

To most of us such a message is clearly a "Trojan" virus and we would consign the e-mail to the recycle bin as quick as you could say "ILOVEYOU."

But Eric Doyle, Technology Editor of Britain's Computer Weekly, says there is always somebody who is going to fall for the virus writer's scam.

"As soon as the virus is sent, someone, somewhere is going to open it. And then instantly it is sent to another 50 people," he says. "One of those is going to open it and the thing goes on."

So why do people fall for it? "Curiosity," says Doyle. "And in the case of Sircam when the virus picks up one or your own file names it looks like a genuine document."

Doyle points not to computer illiterates who don't know their HTML from a jpg as the most likely to be scammed -- but the kind of person who is big into SMS messages.

"People who are message mad," he says, pointing to the vast increase in the use of e-mails which are now said to take up an average 45 minutes of a working person's day.

"Because of the sheer amount of e-mail people are getting -- I went on holiday and there were 400 e-mails waiting for me when I got back -- people will click onto almost anything without realising or even knowing about it."

Jason Holloway, UK general manager of Internet security company F-secure says: "Some people say 'only an idiot user would open an attachment like that, they should be educated in computers so they know better.'

"That's like saying cars are always going to have accidents so we'll do nothing to protect drivers and passengers.

"People need virus protection because it does happen. In real life people have got lots of other things to do and they do click onto these attachments."

Holloway points to the cat-and-mouse battle between virus writer and likely victim and points to the "social engineering" aspect of the messages.

The successful ones like Melissa, he says, are cosy, personally addressed and have enticing messages designed to test out the victim's inquisitiveness.

"The successful ones have very short messages, very to the point like 'look at this very interesting attachment'."

Like Doyle, Holloway doesn't think it is necessarily 'idiot users' who are most vulnerable.

He says there are two types at risk. First the typical home user who doesn't know about hidden extensions.

More controversially he says the other type is IT administrator, whom he likens to a medical researcher catching a germ in the laboratory.

He could be simply playing about with the virus. But more often than not, Holloway says, infection comes from a simple mistake like disabling the virus protection system then forgetting to make it live again.

Doyle reckons the battle between virus writers and the computer industry is about even right now.

He points to a current crop of "sophisticated virus writing" and says the key is in composing an enticing message rather than being a computer whizz.

"You don't need technical knowledge to launch a virus these days, you can buy programmes," he says.

Though the really successful ones do need that little bit of knowledge, he says -- to prevent them being traced and prosecuted.