If you use Windows and you’re curious about what’s using your Internet broadband then the free TCPEye tool will probably help you.
I used it a few weeks ago when something was sucking down gobs of data and making everything else slow. Turns out it was Windows Update, but not on my desktop machine, a laptop on my network was updating.
The odd thing with TCPEye is that CNET Downloads is in the number 1 place when searching for this tool. Reviews even link there instead of the author’s homepage!