Can people steal cable internet from me?
 

I have heard of instances where people steal cable TV. It seems reasonable to me to assume that it is also possible to steal cable internet, after all the cable TV company is the same as the internet company. With recent talk of IP-related lawsuits on the Web and the question of who is responsible for the content running through their wireless internet connections, I wonder if I shouldn't be equally proactive and investigate whether someone could be stealing my internet connection. I have no evidence to support this theory.

Do my concerns have any merit? Is there a simple method to detect this kind of theft?

If you are talking about over WiFi, then yes absolutely somebody can steal your Internet connection.

I do not mean WiFi, I mean over a physical cable connection.

Then they would need to tap into the physical cable or the nearest cable connection box. Either way, there would be evidence of stealing.

Such a thing would be quite possible where I live, in a very old building where I am sure if someone crawled around in the basement they could find the boxes. What I am trying to ask is, is there some way to obtain evidence of stealing? For instance, could I run some sort of software that can scan my internet connection for what other computers are plugged into it?

Look for a rough splicing. Someone who would do that is probably desperate or just stupid and would not make a professional joint. Do you have internet coming through it at all? If not, they could have simply umplugged your cable and plugged it into theirs. Lol-if they were really stupid and it is a broadband connection, they have a router sitting down there. (which I find highly improbable)

I don't think you're quite as defenseless as it seems. Basically, anyone splicing in in front of your cable modem is not going to be your problem. The cable company should be keeping track of what cable modems are allowed on its system. You also wouldn't have to worry about someone running content through this as it technically wouldn't be part of your network.

As for your LAN, I'd stick a router immediately behind your cable modem. A number of routers can restrict what MAC addresses will be accepted as valid, so you can essentially prevent someone from getting onto your network without doing a fair bit of work. MAC addresses are trivial to spoof, but there would be a fair bit of effort to find out what MAC addresses your router would accept, and since you're only using wired connections, it will be that much harder.

If you want to watch your own network, a program like nmap can tell you what IP addresses are in use and a router should have a table what addresses it handed out via DHCP.

Of course you'll need to make sure that the computers you are running haven't been cracked, but that is a different question.