The thing about filesharing is that it's tricky to find out if someone was downloading or not.
However, whenever you share things (as is natural in a peer-to-peer network, the network tries to get you to re-share what you've downloaded), well... the IRAA has these bots up that can track whether or not you've made material available. They can't still prove whether or not you've actually PROVIDED it, but this isn't a criminal suit. They don't have to prove beyond a reasonable doubt. They just have to prove that it more likely than not happened.
You may actually already be on their list Tiana. I don't know, they may still be handing out settlements for $4000. But you won't be able to fight the claim. The governments trying to make it so ridiculously unprofitable to fight a claim here that everyone will go for the settlement.
Pursuing filesharers is actually costing the recording industry a lot more than filesharers in themselves, but the RIAA won't let stupid things like logic get in the way of their persecution.
IP masking is at best a stopgap solution and won't solve much.
You might want to try bittorent. I've never heard of someone getting sued off of downloading from bittorrent.