Ver yearly in my support career
I did a Saturday rota for the computer labs in the Uni I was working at. I walked in half an hour before closing and there was one guy looking at some very anatomically interesting pictures. Being a bit younger then I didn't really know how to deal with it and just said that we were closing in half an hour. He didn't react at all or guiltily close the browser or anything. I should have reported it - hence AC but didn't.
Biting the hand that feeds IT
