There is a big business in special programs written specifically to do employee monitoring. They can get a record of all use on all computers on a network by simply pushing a button. Some employers don't bother, but in medium to large businesses, it is getting more & more common to explore whether folks are 'playing' excessively.

Likewise, there are special programs which are designed to hide what you are doing. Some create 'hidden' folders to store files you don't want to be seen, and some provide a 'boss key' to instantly make what's on the screen disappear. (Not very easy, if they make you sit with your back to the door, huh?)

I strongly suspect the smarter bosses will eventually follow sugggestions made by Wolfgang and Jed and allow a certain amount of personal time, within limits.