What if a user gives his user and pass to others?

Is it possible for one user who has payed his membership to give his username and password to his friends, so they can access my premium content too with just one account?

For example I have a video website with membership plugin.

Mark registers and pays the price for one month membership.

And then Mark gives his username and password to his friends, so all of his friends are watching videos on my website using just this one account.