Spam decreased 8 percent during September, according to a report (PDF) released Monday by MessageLabs.
Among other reasons behind the decrease, the security company cited the apparent demise of California-based Intercage, an Internet service provider alleged to have possibly been used to host command and control servers for various botnets. Intercage's upstream provider, Pacific Internet Exchange, terminated service on September 20; a second upstream provider, UnitedLayer, then terminated service on September 25. During this period, MessageLabs reported a marked decrease in spam traffic.
Looking deeper into the spam traffic itself, MessageLabs found that 85 percent of sexually explicit e-mail spam is sent during the workday. A healthy 28 percent of that is sent during the lunch hours, from 11 a.m. to 1 p.m. local time. Almost all of this is blocked by corporate filters.