So I've been doing some research and checking out the backlinks of sites that rank highly for certain niches, and I've found that many of these backlinks come in do follow comment form, from some pages like this: bitcoincard .org/blog/?page=post&blog=bitcoincard_blog&post_id=sample_yransaction If you look at the comments, there's tons of spam and abuse of anchor text. Now, I know google can penalize your site, but when looking at the majority of sites that I know use SEO, they use tons of backlinks from pages like this and they all rank very high, in spots 1 - 4 usually on google so they must be doing something right; I've found some of these pages to have a pretty good Page authority as well. My question is, how do people find these kinds of sites? There has to be some sort of software or search engine that finds them, most of the time they're from a different country that isn't aware of concepts such as do follow or no follow for their comments. These can't be bots doing it because almost all of them require captcha to post, so what's the deal?