The security with tracking clicks would end microsoft in alot of trouble..... Are you familiar with the AntiTrust law?
On the contrary while trying to track a click google is severly violating user's privacy , Google has no right to upload one's loginid, what version of .net is running on a machine, etc on it's server. If all big corporate decides that clicking on google ad violates privacy of an user using corporate intranet, google can do nothing if coporates stops displaying google ad on their network.
but the fact is not all microsoft employees have that much free time to surf the internet and click google ads. I think their job is more like reserch and inventing things. so only small amount will click the ads though.