Did someone hack my computer?

So, my mom got an email from Verizon saying that someone filed a complaint for copyright infringement. They said that someone using our internet services downloaded Alvin and the Chipmunks: The Squeakquel from a BitTorrent. But, here's the thing...we didn't. No one in our household even cares about Alvin and the Chipmunks so, we have no idea what's going on and we're afraid of what might happen in the future. Can someone tell me what we should do if we were hacked?