Team Hitman Hacker Hijack

Two out of five of my blogs were hijacked by Team Hitman Hacker. I searched everywhere and couldn’t find out how they did it.
I reinstalled on one blog and it seems all right for now. Changed passwords and all.
One blog was updated and one wasn’t, so that didn’t seem to have anything to do with it.
I’m going to try some security plugins now.
Any advice or similar experiences?