What could this sore be from?

Hi guys, I was just wondering if anyone could tell me what kind of sore this looks like?

It seems to not bother this cat here, Oliver. We feel it when we pet him. We have 4 cats however, and it seems that all of them are getting them.

Earlier i tried to touch it and got no response from him, he didnt try to run away or anything. It seems it is scabbed up, but not the whole thing. It is kindof a lost patch of fur. I tried to pull at the fur that is there, and a little fur with a scab? or something came off and it still did not seem to phase him. Its like he doesnt know its there, or its not causing pain. 

Ive been on here before to talk about cat abcesses. We have since then moved from that place and havent had trouble with cat bites or fights. We did however just go through a deworming, because they caught those for a while.

And we also had a dog dropped on us (which is going to a new home soon), so i dont know if theres anything a dog could cause a cat to contract?

I would be concerned about ringworm.  It's hard to tell from your photo though.