obvious: spam cost escalating
From today's WaPo: Spam's Cost To Business Escalates; Bulk E-Mail Threatens Communication Arteries
The flood of unsolicited messages sent over the Internet is growing so fast that spam may soon account for half of all U.S. e-mail traffic, making it not only a hair-pulling annoyance but also an increasing drain on corporate budgets and possibly a threat to the continued usefulness of the most successful tool of the computer age.
Spam continues to defy most legal and technical efforts to stamp it out. The surge has spurred calls for national legislation, but deep divisions remain regarding what constitutes spam and how best to regulate it. In the meantime, spammers, Internet providers, company network administrators and anti-spam vigilantes are locked in a ferocious electronic arms race.
Many spammers have become so adept at masking their tracks that they are rarely found. They are so technologically sophisticated that they adjust their systems on the fly to counter special filters and other barriers thrown up against them. They can even electronically commandeer unprotected computers, turning them into spam-launching weapons of mass production.
...Roughly 40 percent of all e-mail traffic in the United States is spam, up from 8 percent in late 2001 and nearly doubling in the past six months, according to Brightmail Inc., a major vendor of anti-spam software. [Emphasis mine]
As I've said before, the insidious thing about spam is that the spammers bear only a fraction of the cost; ISPs and recipients are the ones who pay to transmit, receive or filter all that junk.