Spam e-mail accounted for 90 to 95 percent of all e-mail in 2007, according to the annual report out Wednesday by Barracuda Networks. This is up from an estimated five percent of e-mail in 2001. The report also found that the majority of business professionals view spam e-mail as the worst form of junk advertising -- worse than postal junk mail and telemarketing calls. Spammers also increased the usage of attachments, such as PDF files and other file formats in 2007.

The study, based on an analysis of more than one billion daily e-mail messages sent to its more than 50,000 customers worldwide, found that 90 to 95 percent of all e-mail sent in 2007 was spam, increasing from an estimated 85 to 90 percent of e-mail in 2006. This growing proportion is even more significant when compared to 2004, when the federal CAN-SPAM Act, which set parameters for sending unsolicited e-mail and defined penalties for spammers, went into effect. At that time spam was 70 percent of all e-mail. In 2001, spam accounted for only five percent of e-mail messages.

"The spam war is a continuous battle between spammers and security vendors," said Dean Drako, president and CEO of Barracuda Networks. "Security vendors now require 24-by-7 defense operations to continuously monitor the Internet for new spam trends and distribute new defensive solutions immediately. This combination can block a new spam attack within minutes of its start -- virtually at zero hour."

Spam raises the ire of business professionals

A separate poll of business professionals was conducted and found that of the 261 respondents, 57 percent view spam e-mail as the worst form of junk advertising, close to double the 31 percent that cited postal junk mail. Only 12 percent chose telemarketing.

The poll also showed that 50 percent of users received five or fewer spam e-mails in their inbox each day. Almost two-thirds (65 percent) received less than 10 spam messages each day, while 13 percent were inundated with 50 or more spam e-mails daily.

The report also tracked the evolving complexity of spam techniques over the past several years, finding that the majority of spam e-mails in 2007 utilized identity obfuscation techniques, in which spammers send e-mail from diverse sources throughout the Internet, thus hiding their own identity from traditional reputation checks that profile sender network addresses. Further, by registering new domains or by redirecting to spam Web domains through reputable blogs, free Web site providers, or URL redirection services, spammers can effectively hide their identities from traditional reputation checks that profile spam Web domains.

Holiday spam: New Years' resolution spam coming next

Spammers are increasingly emulating retail store fronts by tailoring their content around national holidays. For example, Barracuda Networks detected a significant increase in the number of e-mails directing recipients to phishing Web sites on Thanksgiving Day 2007 as scammers rushed to cash in on the "Black Friday" and "Cyber Monday" online consumer shopping sprees. In January, consumers can expect to be flooded with New Year's Resolution spam in the form of weight loss ads and offers for online college degrees.