Few people are genuinely interested in “male enhancement”. The group that might actually buy such a product in response to an unsolicited e-mail is even smaller. So why on earth is there so much spam?

The reason is that spammers have to deluge inboxes to get a hit. Researchers at the International Computer Science Institute at Berkeley and the University of California San Diego took control of a small part of a spamming network this year. In 26 days they sent 348m e-mails, producing 11,000 visits to a fake pharmaceuticals site but just 28 “conversions”, or attempted purchases, worth about $100 each. For those hawking pills, that suggests revenues of about $3.5m a year.