Can my ISP turn off my modem if I use bittorrent?

The interesting thing about bittorrent is that when allowed to run "full speed" it can pretty much saturate your internet connection. By that I mean that you can be both uploading and downloading at your connection's maximum capacity.

That's a fairly unique and uncommon situation. Everything else you've described, even World of Warcraft, doesn't put anywhere near that kind of load on an internet connection.

What I'd be more suspicious of is a line or modem problem. By trying to push the maximum amount of data through your connection you might be pushing the modem into failure. It might have a problem that normally it can recover from so you'd never notice, but at maximum capacity it can't. Similarly, you might have a line noise problem - the telephone lines that carry your DSL connection often have small amounts of electrical noise. Once again, it's possible that your modem is able to compensate during "normal" usage, but can't deal with it at maximum capacity.

Now, I have to admit it certainly is possible that your ISP might have the ability to remotely shut down your modem. They often do have the ability to remotely administer it, so shutting down doesn't seem like that far-fetched an ability. The question is would they?

In my opinion they have other, less drastic ways of dealing with bittorrent.

The problem with bittorrent, from an ISPs point of view, is the same as what I mentioned above: you're maximizing your use of your internet connection. That places an additional burden on the ISPs infrastructure, as they typically aren't built out with enough capacity to actually handle the majority of their users using maximum capacity. As a result, their ability to serve all their customers can be adversely affected by those few who do run bittorrent.

Lest you think they should just build out more capacity, consider the cost - which they would then have to pass on to their customers, meaning you. It's a common, and accepted design approach. Even the telephone company has this same restriction; if everyone picked up their phone at the exact same time the telephone infrastructure could not handle the load. We occasionally see this at times of natural disasters. The good news it that the maximum load scenario is uncommon and things work just fine the rest of the time.

The same is true of the internet infrastructure. If everyone maxed out their connection then it would likely work for no one.

All that being said, the ISPs have other ways of dealing with things like bittorrent that, while somewhat controversial, avoid the all-or-nothing approach of turning you off.

• Throttling: the most common approach is for an ISP to identify the specific packets making up your bittorrent connection, and slow them down. Much like in most bittorrent clients you can instruct the application to use no more than a certain amount of bandwidth, ISPs typically have the ability to do the same. The effect is that your bittorrent transfers will be slower than they could be, but the rest of your internet experience, and that of other customers, is largely unaffected.

• Blocking: an extreme measure is to simply block bittorrent traffic completely. Some ISPs terms of service prohibit it, and they can do that by identifying bittorrent traffic and simply refusing to pass it on. The net effect to you is that bittorrent simply doesn't work.

• Disruption: this is a very controversial approach we've heard about in the press in recent months. It's basically a form of throttling, but instead of slowing down your traffic some of the many connections used by the bittorrent protocol are simply and randomly dropped. The net effect is similar to throttling: your bittorrent transfers are slower.

All of these are just as complex as shutting down your modem when bittorrent traffic is identified, and since they're less disruptive on other internet usage I'd expect ISPs to rely on them instead.

The bottom line: check with your ISP. Read the terms of service and see specifically what is, and is not, allowed. If you find that bittorrent traffic is disallowed, and especially if that's backed up with technology to slow or disrupt it, then your only real option is to find a different ISP that will allow you to use it.