Small businesses are receiving 10 times more spam per user than larger companies, according to e-mail security firm Postini.
Postini said the increasing threat to smaller firms, which usually have less network protection, comes at a time when spam is making up between 75% and 80% of e-mail being sent to all employees.
Postini classes a small firm as one with fewer than 100 employees. Postini said some industries, including publishing, advertising, legal firms, and estate agents, were particularly susceptible to spam, because they widely publicise the e-mail addresses of their employees.
These market sectors 10 times more spam than those in banking, manufacturing, electronics, food and beverages, and pharmaceuticals.
Virus-infected e-mails tripled as a percentage of all e-mail, making up 1.5% of e-mails in 2004, up from 0.5% in 2003. And as much as 1% of all spam is now part of some phishing attempt, Postini said.
Matt Cain, an analyst at Meta Group, said, "More sophisticated, phishing-style attacks will proliferate as bulk spamming scams decrease in effectiveness. We also see dynamic, fast-moving threats such as zombie networks posing particular challenges to corporate systems."
Zombie attacks use the computers of unaware third parties to unleash spam and viruses.
The full Postini report can be downloaded here