An office tower in downtown San Jose, California has long served as home to McColo—a hosting company whose servers in turn have quietly served as a conduit to a huge majority of the world's spam email, scam prescription drug markets and child porn sites. After investigations by the Washington Post's Security Fix blog identified McColo as supreme baddies and shut them down, web security firms saw spam volumes drop almost instantly by up to 75%.
The chart here was sent to the Post by a German hosting facility manager, showing spam's immediate decline after McColo's shutdown (Security Fix has several more charts from security organizations and individuals showing the same thing). It's fun to consider the trickle down effects here—just think of the saved CPU cycles on webmail hosts worldwide who suddenly had 70% less U.S. spam to crunch on, and the energy savings resulting?
Last time this happened, when a similar northern California spam ISP called the "Atrivo" network was busted, it only took spammers a few days to get back to their old ways on another network. So, be sure to revel fully in a world free of Viagra deals, Kenyan wire transfer offers and content sharing proposals from personal lubrication sites (Mark's claim to wealth) while you can. [Washington Post, Security Fix]