I have an ADSL connection with a username and password and dynamic IP.

So I wanted to know if I use my friend's authentication will the ISP know I'm the person using my friend's connection OR will they think it's he who is using the internet ?

Because if authentication is the only thing through which ISP tracks me then I if I could get someone else's information I could browse totally anonymous.

  • What do you mean "friend's authentication"? Do you mean that you need to sign into your ISP before you get an Internet connection?
    – schroeder
    Oct 2, 2015 at 4:31
  • 1
    You can totally destroy your friend's reputation cause he'd get fingered for your online activities. Are you sure you're his friend? Oct 2, 2015 at 5:22
  • Yes we need to sign in. And yeah I said friend because if it is possible then someone else might be able to do this easily if he could get creds of some other person. Oct 2, 2015 at 9:00

3 Answers 3


(A)DSL goes over phone lines, with real phone numbers (even if they aren't hooked up for calls). Changing your credentials won't change your house's phone number, any more than unplugging one landline phone and plugging in another would change the number.

Additionally, your router has several unique identifiers and presents at least one of them (WAN MAC address) to the ISP. You may be able to modify those, spoofing another user, but simply changing creds won't prevent them from identifying you.

The first point is probably the bigger problem, though. For a DSL provider, looking up a name and address by phone number is dead easy; in most cases, that's how they bill you.

  • Well the usernames are the phone numbers. Like my username is 331100**** and my friends is same except the last 4 digits so when I connect it would still get my number even though I logged in using his credentials ? Oct 2, 2015 at 8:59
  • In that case it might not even be possible to use the wrong credentials. The DSL provider sees the phone number before they see anything else. Like, if a website is tracking you by IP address, logging in with somebody else's account doesn't help because the IP address is lower-level info. In this case, the phone number is lower-level than the IP address. It's possible they would let you supply the wrong phone number, but they would still identify your connection by its real phone number. If they didn't, packets meant for you would go to your "friend's" modem.
    – CBHacking
    Oct 2, 2015 at 18:15

In many cases user name and password are used for billing if you have caps on how much traffic you can do like pay per use, or if you have special services associated like unlimited traffic.

Sometimes they might use the same information for network authentication and in that case it might be associated with your cable router / ads DSLAM.

But if something nasty is done using the networks both phone numbers will be in scope for investigation as they will be correlated what phone number was used for the account they will notice 2 coper numbers associated to the user name.

Also you will be probably violating your terms of usage with the ISP. Might be considered crime if you mess with the billing system Or fraud if you enable a paying customer to pay less.

I strongly advise you not to go that path and just satisfy the curiosity of your question with the answers here provided do not try it.

If you share the same DSLAM the probability of being able to do what you wish is high and it depends on the service provider settings.

You are always trackable in any situation but you will cause the ISP security to be more angry as they will have extra work... :P

Normally it is not possible to change credentials even if you share the same ISP but you hare connected to different DSLAMs...


Your ISP can only track you when you put clear data through your router/modem, considering they're the ones that own it and monitor you through it. This can easily be prevented by using a VPN which sends encrypted data rather than plain data that can be read by your ISP.

I don't have any experience with ADSL, but by the sound of it, if you're logged into your friend's account (or whatever it is) then I don't see how they'd find out you're the person using it unless when you log in it's with your IP that they know is yours and not your friend's. Just a wild guess.

  • Check l1thal's answer. Oct 2, 2015 at 1:33
  • Ours is practically the same thing except for the fact that mine was posted first. You can prevent your IP from being logged by using a VPN as well.
    – R. Goff
    Oct 2, 2015 at 1:43
  • if you're logged into your friend's account (or whatever it is) then I don't see how they'd find out you're the person using it see CBHacking's answer. The ISP knows who is the person connecting by looking up who is the owner of the landline, not from the submitted credentials. Nov 26, 2020 at 17:02

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