A lot of my sites were hit with a penalty for unnatural outbound links because I did not pay as closer attention to the links being inserted into guest links as I thought I was. I had been accepting two or three guest posts a week on these blogs since 2008 so as you can imagine there were a lot of links to go through. In the end I have deleted around 200+ links from each site and have only left links to Wikipedia, social media profiles, and URLs that are actually related to my niches.
I also installed a plugin that turns all my links to Nofollow.
So far one of my sites has had its penalty removed.