Companies' increasing fear of spam email being a vehicle for virus attacks will see the global spend on protection software more than doubling in four years, research shows.

Spam and junk mail has replaced employee Internet abuse as the main explanation of organizations' rapid uptake of Internet filtering software.

Less than two years ago it was the legal debate surrounding the misuse of the Internet by employees and porn surfing that led to the speedy adoption of content management software, but today the real nuisance is the constant flow of spam.

Worldwide revenue for content management software is expected to hit US$4.8 billion in 2006 compared to $2 billion in 2001, which is indicative of the high level of employer concern, according to IDC.

Piggy-back viruses Managing director of software provider SurfControl, Charles Heunemann said spam is not only a drain on network bandwidth and staff productivity, but is emerging as a security problem with the emergence of blended virus threats.

"It is only a matter of time before blended threats such as Nimda begin piggy-backing off spam; it is up to IT to educate users not to respond to spam and encourage a reporting process whereby users can notify IT to stop further spam coming through," he said.

An IT manager who wished to remain anonymous said it is impossible to manage the spread of junk email by employees, particularly chain letters.

However, respondents to research from the University of Western Sydney rated chain letters as more annoying than porn.

Chain letters top the list of objectionable e-mail, followed by credit offers, money-making email and then porn.