I don't know if anyone remembers, but about a week ago WatchMojo got hacked by someone by the name of Poodlecorp. Apparently the same guy hacked Leafy today, and renamed every single one of his videos to "hacked by twitter.com/poodlecorp."
There's been a lot of leafy fans giving Poodle death threats in the comments, although I personally find it funny because they usually have Minecraft icons and I'm pretty sure he won't read those regardless.