It's a juvenile something, which makes it harder to ID. It is probably either a costellariid, which will eat tiny worms, or a fasciolariid, which will eat other snails. It could also be one of the elongate Nassarius species. There's a good chance it's not a bad guy, but flip it over next time you see it. If it has a dark red or maroon animal, it's a fasciolariid, and you'll likely want to remove it. If you can catch it and take photos of the apertural view in a dish of water, I might be able to narrow it down for you.
Cheers,
Don