The figures, released today, show that firms in all sectors were severely hit by viruses and spam last year, but manufacturing was the most affected.
Eighty-two percent of e-mails received by the sector were spam, while one in every 26 e-mails contained a virus.
Firms in the recreation (74%), retail (64%) and chemicals and pharmaceuticals (64%) sectors also suffered badly from spam, while government and public sector e-mails fared better, with only 19% of their received e-mail being spam.
According to MessageLabs, viruses were the biggest problem among not-for-profit and healthcare organisations, where one in every six e-mails contained malicious content. The government and public sector (1:9), retail (1:10), education organisations (1:12) and building and construction companies (1:14) also sustained regular attack.
The sectors best protected from viruses were professional services, such as legal firms, where the ratio was one in every 38 e-mails, and financial services companies who received a virus every 29 e-mails.
"The severity of these attacks is unsurprising, as 2004 marked a sea-change in terms of e-mail security threats to business," said Mark Sunner, Chief Technology Officer at MessageLabs. "The convergence of viruses and spam is now dominant – almost all viruses released in 2004 contained some additional component allowing the infected machine to become a spam sending zombie. So it is of little surprise that all sectors of 'UK plc' were so badly hit".
"What is notable is the spread of the attacks however," he added. "In previous years the companies most affected tended to be those dealing mostly with less-protected home users. This year there does not appear to be such an obvious trend. That said, those companies most aware of the need to protect confidential information in their business – such as law firms and banks – do tend to have the most sophisticated approach to their security."