We've discussed recently the growing problem with image-based spam. Today, we have some interesting findings from Commtouch, an e-mail security vendor regarding this growing problem:

* Toward the end of the second quarter, there were significant peaks and troughs in the distribution of image spam. For example, on May 29, Commtouch found that image spam constituted 30% of global spam, dropping to almost zero six days later. Seven days after that, on June 10, image spam hit another peak of 22% of all spam, dropped again, and then hit another peak of 15% on June 24.

* Image spam is significantly more impactful on both bandwidth and storage requirements than text-based spam. For example, Commtouch estimates that when image spam hit its May 29 peak of 30% of all spam for the day, 70% more bandwidth and storage were required to deal with image spam on that day.

* The average image spam is 18KB compared to the average text-based spam that is only 5.5KB.

What these findings point out is the critical need to block spam as far back in the network as possible. That means that organizations need to use either in-house perimeter defenses in order to block image spam before it has to be processed using CPU-intensive spam filtering techniques, or they need to use a managed service that will prevent e-mail from reaching the network and thereby consume additional bandwidth and storage.

The emergence of image spam also points out the seemingly never ending game of cat-and-mouse that spammers are playing, pushing 'pump-and-dump' stock schemes and other scams using randomized image spam as the delivery vehicle, a relatively new technique.

In addition, the growing problem with image spam continues to underscore the critical need for home users to maintain antivirus and other defenses in order to prevent their systems from becoming zombies that are the source of most image spam.

Michael Osterman is principal analyst of Osterman Research.