By hijacking a working spam network, a group of researchers have discovered that it takes 12.5 million spam emails to get just one response. So why do spammers keep on sending junk mail in spite of the miserable response rates? Apparently because even though the vast majority of people ignore them, those who actually order products via unsolicited mail end up making it a profitable activity.
The research team managed to hijack part of the Storm network earlier this year for a month-long period, and used it to send spam campaigns from over 75,000 compromised machines. Despite sending almost 350 million email messages, only 28 sales resulted, though scaling things up to the full Storm network capacity the researchers estimate spammers are netting about $7,000 a day or more than $2 million per year - apparently not as much as earlier predicted but still well above operating costs.
Improved filtering technology has done a lot to lessen the burden of unsolicited mail, but spammers keep working on new techniques, and in the end the only way to stop spam completely is to stop responding to it. The full PDF version of the study is available here.