A number of factors have contributed to the situation, and what they all have in common, unfortunately, is that spammers are getting much more sophisticated.
Botnets have gotten so sophisticated that theyre almost impossible to shut down. This surge of spam is, perhaps, a show of strength, as well as the botmasters exercising the fruits of their efforts developing an underground network.
How big is the surge? Postini, the largest hosted secure e-mail provider out there, handling over 1 billion messages a day, ought to know, and know in real time. The company says spam volume is up 120 percent over the last year, but 59 percent in the last two months. Thats in line with numbers Ive heard bandied about elsewhere, and its a huge rate of increase.
Another factor is what security vendor Borderware calls "anti-anti-spam spam," meaning spam that attempts to defeat anti-spam measures. Spammers have learned all sorts of tricks.
For instance, if a recipient rejects the message, they are attempting to resend the message like a real mail server will. Spammers historically have had naive mail transfer programs that send a message and then move on, ignoring any errors.
Many anti-spam systems rely on this characteristic to employ a technique called graylisting. They reject the message once from any sender they do not recognize and accept it on resubmission, whitelisting the sender at the same time. This all assumes that a spammer wont retransmit. Graylisting seems headed for the ash heap of anti-spam history.