In the majority of medium to large companies I've worked in, there was a porn ghost built into the software.
So that the Head of IT, or some other senior individual, would immediately be made aware of those logging onto dubious sites.
The Terms and Conditions of your employment (signed by all) prohibited such activities, and the result was summary dismissal.
Although the names of the 'culpits' were never made public.
Just maybe, the star performers only got a yellow card...