Recently, I experienced a very strange behaviour on our Wi-Fi network: we share a Wi-Fi network using a simple router. One of us pays the bills and he's the one, who got the management account from our ISP.
So if I want to log in to look at my mobile bills (the ISP does both, mobile and wired Internet stuff; I have my own account) I am logged in automatically with his internet management account, from different devices over the Wi-Fi.
How can this be possible? I cannot find useful information about that. As I know from a programmers point of view, simple session management should avoid such a behaviour (e.g. cookies). Does it mean that the session management is only server-sided and just bound to IP (server, programming issue)?
I think the ISP bound the external IP of our router automatically to this single management account, which would be, in my opinion, a very big issue (watching bills, changing address data and so on).