The number of worldwide email inboxes is expected to increase from 505 million last year to 1.2bn in 2005, a growth rate of 138 percent, according to analysts at research firm IDC.

"Wireless access through email devices and network services will offer new ways for email users to remain connected longer while on the move," said Mark Levitt, research director of IDC's collaborative computing programme.

According to IDC, by 2005 36 billion person-to-person emails will be sent on a daily basis.

"Email usage is growing despite challenges from market substitutes like instant massaging and virtual workspace [which] often fall short of matching email's ease-of -use and global reach," said Robert Mahowald, senior analyst at IDC.

But if researchers at virus security company MessageLabs are right in their prediction that within seven years one in 10 emails could be infected, then the number of machines likely to be contaminated by each virus does not bear thinking about.

Mark Sunner, chief technology officer at MessageLabs, warned yesterday that the volume of infected mail circulated could become so great that people without sufficient protection will stop using the internet altogether.

"The escalation in email-born viruses, and the spread of hybrids that attack on many different fronts means that, while the internet will not collapse, it will certainly cease to be usable as a safe and credible means of communication for business and home users," said Sunner.

MessageLabs warning does seem a little over-hyped, but should perhaps be viewed as a warning to users to ensure their systems are properly protected.

MessageLabs alone stopped 333,000 copies of the SirCam virus.