Another Noob Question

[BigA]

Hi everyone. I've got a quick question. Yesterday I bought some turbo snails (I think. They do have conical shaped shells). Once I brought them home and accimated them, into my tank they went. Almost instantly they got attcked by one of my hermit crabs (I'm not sure what kind it is. It has greyish legs, with red tips). I have a ton of extra shells in there and have had since the tank was started up. I seperated them this time, but when I awoke this morning it had happened again. I thought hermits were supposed to be reef safe? Is this a bad apple of a crab? A bad species? Is this going to happen every time I put some snails in the tank? Can this unprovoked attack be prevented?