This is a lesson for creating backlinks. Backlinks are the number of links pointing back to your site content. The more links you have the more credible you are to search engine. And many people exploit this system, but most of the time when you exploit it the wrong way, it can end up hurting you more than helping you. One of the way things can go bad for you when trying to create credible backlink, is getting linked from a site that is de-indexed by google.
If google decide to de-index a website, then it must be in serious violation. And sometime, just for being associate with them, it can cause your website to lose ranking, and it definitely will not help you improve your ranking on google.
Be sure that when you are creating backlinks, ensure that it is a credible site and it is indexed on google. And you can perform a quick search from google.com to see whether they are indexed or not.