In reply to Trangia:
A theory from https://www.stopforumspam.com/forum/viewtopic.php?id=2799
"The homeworkers idea is pretty accurate to some extent. These shady SEO sites claim to give a site owner thousands of backlinks for a set dollar amount. They then use automated software (xrumer mainly) to bombard forums and blogs. Since so may sites have anti bot registration protection, they pay live humans in 3rd world countries to do the spamming. Humans can beat the registration questions much easier than a bot. They pay them a pittance of around $1 for every 1000 links. The ones doing the work are desperate for any cash. There are others that are in this on their own, and set up all kinds of filter sites leading to their money site, but I tend to believe that a large portion of them are as you said- desperate and scammed homeworkers.
I blame the SEO sites more than anyone. They perpetuate the lie that one must cheat to get better Google and other search engine rankings. In all honesty, there is very little real SEO that can be effectively done on a forum. The forum is dynamic and you can't control what people post or their topic titles, etc. Google will find the site anyway, and the site's content is more important. The SEO'ers perpetuate the lie that backlinks and keywords are absolutely necessary. So many green forum owners fall for that crap and hire the SEO "experts", starting the spam cycle all over again."