IP Technical question

[Paul Barnfather]

>>    If so, how is an ISP able to determine exactly the individual
>>    computer that accessed a particular website?
>
> Given an IP address and a timestamp, the ISPs records will show which
> account (ie: paid for service) was allocated the IP address. Depending
> on circumstances, this may identify a single computer, or it leave a
> large number of possible machines implicated.  There's then a separate
> question as to whose fingers were on the keyboard -- or who was
> controlling the program running on the computer....

How reliable is the mapping of subscriber account to the point of
physical access? The reason I ask is that I recently moved house to a
house with a different phone number, but on the same local exchange.

At the new house I was somewhat surprised to find that my ADSL modem
happily logged on to my old broadband provider using the login
credentials from the old address. These login credentials were made up
of <old phone number>@<old broadband provider>.net and a random
password. This was before any account transfers, etc had taken place.

Given the above, can I assume that it is possible that another person
(using ADSL login and password) could log in to my broadband service
from any other phone line?

If that was to happen, would any such activity by a third party be
associated with the physical phone line (which would presumably be OK,
as they could spot the discrepancy), or my broadband account (which
could potentially be a bad thing)?

Perhaps someone familiar with the process of logging on to an ADSL
account could clarify how it is possible for me to access my broadband
service from the "wrong" phone line and whether this introduces
additional risk that activity on a broadband account could be
attributed to the wrong person/account.