I've had one in my tank before and all it did was eat algae. I haven't heard of it eating corals and if there are any reports of it doing so, my first guess would be incorrect identification (but you never know, so read up on them and keep an eye out for problems). In fact, there is a guy selling some on my local forum right now and they are being bought up pretty quick.
Scutus scutus, aka elephant snail. Algae eater. I have them in every one of my tanks, they are nocturnal, and clean the algae off the rocks. Reef safe in my experience.