If you have a 3-user license for NOD32 or Kaspersky - what happens when you install the fourth? They all use a single user/key. I'm sure the software obviously calls home, but how does it know you're using it on four systems?
What if the fourth install was never on at the same time as one of the other installs?
What if the fourth install was never on at the same time as one of the other installs?