The Register’s Interview with a link spammer.
When Sam begins a spam run, he has one target, though he’ll accept any of six. Principal one: come top of the search engines for his chosen site’s phrase. “But you’ll accept coming in at 1,2 or 3, or if you come at 8,9 or 10. Actually, 8, 9 and 10 have better conversion rates. I don’t know why. Maybe the eyes fix on it when you scroll down the page.” And the cost of doing it? Once the code is written, pretty much zero. “Bandwidth is cheap,” he says. “You set it going in the evening and come back in the morning to see how it’s gone.”
So what beats them? Sounds like captchas (those distorted images requiring a human to type a letter)
So what does put a link spammer off? It’s those trusty friends, captchas – test humans are meant to be able to do but computers can’t, like reading distorted images of letters.
There’s several WP plug-ins that will do them; I haven’t tried it yet. But I will soon.