Out of around 500 messages in my spamtrap right now, slightly more than 23% have the word 'penis' in the Subject line. Almost 28% contain the word 'penis' in either the Subject or the body of the message. Neither of these figures include cases where a different word or an obfuscated form has been used, nor does it include Viagra and Cialis spam. All summed up, spam playing on male insecurity probably makes up more than 50% of the total load today.

The click-thru rate for this kind of spam is fairly low. A New York Times article about spam effectiveness puts the click-thru rate for 'pharmaceutical spam' (which might include magic penis pills and similar snake-oil, or might be limited to Viagra et al) at 0.02%, hence the perceived need to send it out in huge volume. This probably translates to low returns, making penis enlargement spam the spam you run through your botnet when you haven't anything more lucrative to send. Moreover, spam filters will make short work of such obvious junk: only a tiny percentage will ever come anywhere near any user inboxes.

If penis enlargement spam is really the carrier signal of the spam world — a kind of low hum on the line that carries no useful information — does that mean the botnet herders have excess capacity? Suppose you built a botnet and nobody came? What then?