I fixed a 'dirty' pc in a small office with 3 people. The offender was one of the two bosses, the other one did not like that.

I added porn filter on there router.

I once worked in a small office and was told a story about a previous employee who offered to hold down the fort while the rest of the office went to lunch. While they were gone he watched porn. Knowing that activity was logged, he was clever enough to use someone else's computer. He was not clever enough to consider that he had just verbally confirmed to a dozen coworkers that he would be the only one in the office at the time.