The term "spam," in its e-context, references the Monty Python sketch in which a restaurant adds spam (canned spiced ham) to everything, whether you want it or not. Spam, spam, spam, spam, spam, spam, spam.
According to Jeffrey S Rosenthal's book Struck by Lightning: the Curious World of Probabilities, spam brings in fifteen responses for every million emails sent out (data current in 2005). It costs a dollar to have someone send out ten thousand spam emails. A hundred dollars for a million. Fifteen responses at ten bucks each, we're talking fifty dollars profit. Plenty of digital waste for a meagre profit. But there are other ways to snag customers.
Search engines rank websites based on a number of factors, most of which they don't divulge. But if a site is linked to from multiple outside sources, that's a good thing. Higher ranking.
So spammers submit comments on websites and include links to the site they're paid to promote. The link might be in the comment, or show up as part of the commenter's ID.
As of February 2011, according to Wikipedia, there are more than 156 million blogs in existence. Just like with hand-written journals, back when people still did that, there are plenty of strong starts. But friends fail to gush. Fame doesn't come, like it did for Stuff White People Like or PostSecret. Magazine editors don't email. The hit counter remains discouragingly low. The blogger loses interest. But the blog remains, gathering digital dust.
In come the spammers. Leaving comments on posts. Especially older ones. The blogger might only check her site periodically, and probably doesn't comb through all of her old entries. The comments stay. Their links are detected by search engines, which rank their sites that much higher when people want to find cheap watches, knock-off fashions and boner pills.
Here at Beams, authors are notified any time someone comments on one of their pieces. The newest comments are displayed on the side bar. When spam comes up, we delete those suckers pronto!
But one persistent spammer seems to have an affinity for Sr. Chela's Shut the F**k Up and Practice: Engaging the Collective for our Growth. Poorly worded comments appear in this particular post on a daily basis, and are unpublished as quickly as they appear.
Why poorly worded? Because you need a person to create an account on this site, and many others. A 2011 Cisco Systems report says spammers primarly come from countries whose first language is not English. Poor people. From poor countries. Working for cheap. And leaving comments like this:
"I placed on the web site of the feedback, and share your blog the author's big believers understand. I will recommend my friends to have a look, look forward to the new content."
If you have an old, dead blog, it may be hosting parasitical spam like that.
And that's why spammers leave comments on blogs. Spam, spam, spam, spam, spam.