Leaching off my internet?

I have hughes net and I just got a new laptop. One computer of mine seems to run slow like the internet is always choked back which i wonder if it has to do with my past use of p2p programs. My laptop was running fast with good speeds until i transferred my itunes library via mp3 dvd. I also used a site beemp3 to download one song. Is it possible that the use of either of those two could have gave someone access to my internet and they could be sucking all my bandwidth? If so how do I correct it? Thanks!