Spam continues to gunk up the Internet's arteries.

In September, more than 17 percent of all e-mail traveling across the Internet could be classified as spam, according to data collected by U.K. e-mail service provider MessageLabs. The company's figures are presented in its latest monthly report.

"In speaking with our customers six to eight months ago, (the concerns) were virus, virus, virus. Now, spam is priority No. 1," said John Harrington, director of U.S. marketing for MessageLabs.

The company tracked some 63 million messages as part of its anti-spam service and found that about one in every six was junk e-mail. That adds up to more than 11 million of the messages counted.

MessageLabs' data comes as state legislatures are trying to find a regulatory solution to the problem and fed-up consumers are taking spammers to court. Even direct marketers are upset with the junk e-mailers, who seem to be souring consumers against all unsolicited e-mail marketing.

MessageLabs' earlier data, from a smaller number of customers testing its anti-spam service, showed junk mail accounting for as much as 50 percent of all e-mail messages for some companies.

Those numbers still hold for certain industries, said Harrington. In particular, the new MessageLabs data shows that the manufacturing and engineering sector was the industry hardest hit by junk e-mail, with about 26 percent of all e-mail classified as spam. Health care, the next most inundated industry, had 21 percent of all e-mail classified as spam.

In addition, companies in the United States have a much higher load of junk e-mail to bear than British companies, which make up the bulk of MessageLabs clients.

"Seventeen percent is a good measure of the overall impact, but for companies in the United States, spam is more of a problem," Harrington said.

MessageLabs also released its monthly data on the prevalence of e-mail viruses.

On average, about one in every 210 e-mail messages processed by MessageLabs contained a virus. The Klez.h virus accounted for more than half of all malicious program attachments intercepted by the company.

While mass-mailing viruses account for a far smaller fraction of e-mail on the Internet compared with spam, the self-spreading programs can be a lot more damaging. Despite that, companies have begun treating the nasty little denizens of the Internet as the cost of doing business.

"People are becoming desensitized to e-mail viruses," MessageLab's Harrington said, pointing out that Klez.h was the most prolific virus to date, but also that it garnered a lot less media attention than the LoveLetter virus.