That only affects history and temporary files on your computer. If they're running a proxy server or something similar it's pretty easy to track what has been going on.
We have an extremely healthy computing network and IT forensic people, whatever I do is extremely visible. The nice thing is they are pretty liberal with what we can do, but if we cross the line we are done. Unfortunately Puff is on the no-no list while strangely my homebrew forum is gtg. Oh well, I still hang out on Puff via iPhone while at work, muuhaha.