A linguistic question - why is this spelled with a "k"? I assume this is derived from "ocupación" - the "k" looks funny to me as someone familiar with but nowhere near fluent in Spanish.
If you okupas you always ocupas. But you can ocupar without okupar.
The k differences the political movement from the physical act of using a property which is not yours. Okupas don't promote squatting in a small owner property. They promote using unused properties from banks.
In fact in Barcelona there are la Oficina d'okupació:
That'd be my guess at least. Maybe someone could track down a definitive answer.