Every month I can allow only 3-4 computers (browsers, actually), to access the site as paying subscribers with the same user/password (paying subscribers are all in the same tiki group).
I am thinking I could limit the browsers a user can use each month (via cookies?) to 3.
When a registered user connects to xxxxxx.com, we set a cookie in his computer, and we register his computer/browser as "authorised computer for 30 days"
Every time he comes back to xxxxxxx we read his cookie to we check if he is an "authorised computer". If he is already authorised we let him log in, if he is not we check how many "authorised computers" do we have listed from him. If we have less than 3 authorised computers we register his new computer and let him log in. If he already has 3 authorised machines no deny the login.
In case a computer is not used in 30 days we drop it from the list of authorised computers.
I will also need a "control panel" so I can manually remove authorised machines from the list (I guess I will have to make some exceptions as users buy new computers, delete cookies, travel...), or change the number of authorised devices to 4, 5, 2...