From NYTimes Magazine (a longish article):
The crush of the [spam] messages on the world’s networks is now numbered in billions per day. One anti-spam service measured more than five million unique spam attacks in December, almost three times as many as a year earlier. The well is poisoned.
Spam is not just a nuisance. It absorbs bandwidth and overwhelms Internet service providers. Corporate tech staffs labor to deploy filtering technology to protect their networks. The cost is now widely estimated (though all such estimates are largely guesswork) at billions of dollars a year. The social costs are immeasurable: people fear participating in the collective life of the Internet, they withdraw or they learn to conceal their e-mail addresses, identifying themselves as firstname.lastname@example.org or email@example.com. The signal-to-noise ratio nears zero, and trust is destroyed.
”Spam has become the organized crime of the Internet,” said Barry Shein, president of the World, one of the original Internet service providers. ”Most people see it as a private mailbox problem. But more and more it’s becoming a systems and engineering and networking problem. It’s depressing. It’s more depressing than you think. Spammers are gaining control of the Internet.”