Discover multiple users on the same account

Question

I have some kind of web application - you pay for the account, and then you can use the services it provides. Now I would like to discover that two or more users are using the same account - and they are warning the user or disconnecting this account.

I really don't know where to start, so can you tell me something? Is a solution ready for this problem (possibly open source)?

I could compare IP addresses, but this can lead to false positives (perhaps the user accesses my web application from his mobile phone and after a few minutes from his computer) ...

Answer 1

You can do something very simple - when you enter from one place, you automatically exit from all other places. This will not solve completely, but it will make it more annoying for 2 or more people to share the account.