Minecraft Server Got Hacked?

I was casually playing on a friend's minecraft server, and all of a sudden the server closed and reopened into a new world. We all got kicked and came back on. I typed "hack!" and I got banned instantly. Later, when I looked at the description, it said it was hacked by "Elvix Society. What's going on?

I know. Is there any way to reverse this?

Ahck

Elvix society just struck our server today too >:( the owner is trying to get the server back but i don't know how he will or how long it will take.