ok a little backround info first: where I live cable internet doesnt use pppoe or anything like that, you just plug it in and go. a few weeks ago myfriend canceled his cable internet, and all they did was cutr the wire outside his window that lead to the modem. today i went over to his house and split the cable going to his TV, and connected up the modem. presto, the internet worked again! Now does anyone know what the chances are that they have the mac address or serial number of his modem stored somewhere so they can detect this unauthorized usage and trace it back to him? any other important things to know?

What cable provider is it? AT&T broadband locks in your account to a specific mac address of you ethernet card, and it keeps track of both the serial number and mac address of the cable modem. I don't know about other service providers. And AT&T doesn't use pppoe either.

It's videotron in montreal (canada)

i dont know about that specifiec co. but you can bet they have something. i wouldnt do it if i was him. they have gotten smarter

I had my cable provider cut off both internet and TV over a year ago. I still have both and have even told them several times when they call to get me to sign up for the service again. I don't think they can turn it off.

Depending on how organized they are, they probably wouldn't even find out. I imagine the worst they would immediately do is turn it off if they found you were an unauthorized user. At that point I would not suggest pushing your luck any farther.