The overall volume of bad bits being pushed across the Internet soared in 2009, primarily due to an increase in image spam and malicious documents attached to junk e-mail, Google's Postini group said in an analysis published last week.

More than half of the messages are fake notices of underreported income from the U.S. tax authority, the Internal Revenue Service, and another third are fake package tracking tickets, Google stated in an analysis posted on its enterprise blog. The jump has led the number of spam bytes per user to more than double in a year, said Adam Swidler, senior product manager for Google's Postini group.

"We have actually seen volumes that we haven't seen in two years since the Storm worm," he said in an interview with SecurityFocus.

The Storm worm dominated much of the spam and virus landscape in 2007, as did image spam, which increased through late 2006 and then declined at the end of 2007. By 2008, image spam had largely died off and the Storm worm had become a much smaller threat.

The recent increase in spam volume means that companies that handle spam filtering internally will have to pay more for bandwidth, said Zwidler. "You have to buy capacity for the largest spike," he said.

Zwidler also cautioned companies to take care in setting their filtering to allow any e-mail from their domain. Spammers are starting to take advantage of domains that are completely whitelisted to bypass spam filters.

"There are a lot of spam services where they are spoof your own domain," he said.

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