Depending on your employer, if they have an IT department and are a medium to large company, they can literally watch your screen. Even record all your keystrokes. Maybe he is reading it, so what, you are sober.
I can tell you two VERY interesting stories about a large company and I know for a fact they can find out anything they want about an employee. But I will add that they will not waste a ton of time on a wild goose chase to obtain "gossip". They do serve a legitimate purpose and are being monitored themselves. PM me if you'd like to hear them, or if someone else wants me to post I will. I will leave it anonymous so no company nor person is singled out.