Egyptian security researcher Ahmed Aboul-Ela reported vulnerability that allows him to delete any comment from all Yahoo Services, including Yahoo News, Yahoo Sports, Yahoo TV, Yahoo Music, Yahoo Weather, Yahoo Celebrity, Yahoo Voices and more. The vulnerability has been fixed by Yahoo Security Team after Ahmad reported them few weeks before. An attacker can delete comments from a post, only if he is the first commenter to comment on that post, and can delete any other comments posted by others who post after you.
Source: https://thehackernews.com/2014/05/vulnerability-in-yahoo-websites-allows.html