One week after rogue ISP McColo was shut down spam levels have yet to return to normalcy. But security experts are under no illusions that this represents anything more than a temporary reprieve, which will probably come accompanied by a change in tactics by spammers.The volume of spam in circulation fell by as much as two thirds after upstream providers pulled the plug on McColo, which harboured many of the command and control servers that controlled the world’s spam distribution. Immediately prior to McColo’s shut down, these three botnets were ranked first, second and fifth the world’s most prolific sources of spam, altogether responsible for nearly 70 per cent of junk mail, according to net security firm Marshal8e6.
http://www.theregister.co.uk/2008/11/21/mccolo_shutdown_analysis/