Top ten most blocked categories are focused on providing a safer Internet experience for students and children. Blacklists are typically used when there is no desire to block an entire category in principle, but there is a focus on preventing traffic to specific websites based on a combination of their popularity and content. Facebook.com, MySpace.com and YouTube.com are the most trusted sites in their category. PhishTank is the free community Web site where anyone can submit, verify, share and share phishing data.
Source: https://thehackernews.com/2011/02/opendns-2010-report-web-content.html