] we've heard confident assertions that there are really
] only a dozen or so "kingpins," and equally confident
] assertions of 200, or 1000. Frankly, I think the number
] is probably larger, because cases against allegedly large
] spammers don't seem to affect the overall volume of spam
] out there. If there were only a few, those cases should
] make a noticeable difference. Or, it could be true that
] there really are only 200 at any one time, but it's very
] easy for others spammers to enter the business.

The FTC is looking at authentication systems like SPF to address the spam problem. They don't believe law enforcement can do it.

The FTC's View on the Spam Problem (washingtonpost.com)