The volume of spam rocketed in December to account for a record 94% of all Internet-sent e-mail during the month, a message security company said Wednesday.

"This continued rise in spam levels is threatening the viability of e-mail for businesses and is sapping the productivity of hundreds of millions of workers around the world," said Daniel Druker, Postini's executive VP of marketing, in a statement.

The portion of e-mail that Postini pegged as spam reached 94% in December, an all-time record. The company blocked 25 billion spam messages aimed at 36,000 clients that month, an increase of 144% over the same month in 2005.

Druker laid much of the increase at the feet of the "Happy New Year" worm -- aka Nuwar, Mixor, and Tibs -- which was heavily spammed to users before and during the last weekend of 2006. Postini blocked more than three times the number of Happy New Year worm messages than the next-most spammed malware, a variant of the long-running Netsky family.

Spam is more than a nuisance when it reaches unprecedented levels, Druker said. "Just 15 minutes per day dealing with the increased volume of spam can cost companies $3,200 per employee per year. [That] adds up to tens of billions of dollars of lost productivity around the world."

Postini also said it expected spam levels to continue climbing during 2007 as even more computers are linked to high-speed broadband connections. Those machines are the ones typically targeted by attackers who hijack systems for wide-flung "botnets," or collections of compromised computers.