I was having a little wander....I think it was near winterhold...when I stumble upon a stray dog who had just killed a bandit. It didn't attack me so I just thought meh and carried on, but it started following me! It even stayed with me when I fast traveled, and fought my enemies!

Has anyone else encountered him? He'd still be following me now if he hadn't been murdered by my follower due to a stray fireball

I've encountered two of them. The first one I told to go home. Then I encountered another. I eventually told that one to go home as well.

I just can't stand the thought of taking them into dungeons with me. They might die.