You have to be really careful with these, as well as companies trying to sell you SEO services which will inadvertently do this as well. This is why I would never use some rinky dink small SEO company to do work on my behalf. A business I work for got into a lot of problems with an SEO company we were using to create backlinks. They were putting our ads on sites that also had ads for child porn and bestiality on them. Worse yet, whatever method they were using to submit us, they could not get us off these sites for some reason. It was a mess.