Broadband-connected computers commandeered by spammers drove a 30% increase in the amount of spam headed to consumer e-mail boxes and corporate networks, an e-mail security firm says.

Remotely controlled armies of computers, called zombies, spread to all regions of the world in 2006, with as many as 8 million computers spewing billions of junk e-mails on any given day, Commtouch said Wednesday in its 2006 Spam Trends Report.

New sophisticated spamming techniques overcame traditional anti-spam methods, such as content filtering, heuristics, and IP address blacklisting, the report said. Among the more effective new techniques was the use of image-based spam, which is much harder for security software to detect than text-based spam. The former accounted for 70% of the bandwidth taken up by spam this year, Commtouch said.

"Spam outbreaks got bigger, faster, and smarter during 2006," said Amir Lev, Commtouch president and chief technology officer, in a statement.

On average, spam accounted for 87% of e-mail traffic this year, a 30% increase over a year ago. Spam rates, however, varied considerably by user and organization. Some small enterprises had spam rates as low as 45%, while large free e-mail providers got pummeled with rates as high as 98%. In general, business e-mail accounts received a smaller percentage of spam than consumer accounts.

Zombies accounted for 85% of spam circulating the Internet, Commtouch said. Half of all phishing attempts involved spam posing as e-mail from eBay or PayPal.

On any given day, from 6 million to 8 million zombies were active, with spammers operating individual armies of as many as 200,000 hijacked computers.

Commtouch is not the only security firm to report a big increase in spam. Last week, IronPort Systems said spam volume soared 35% in November.