Help needed urgently

My friend is a software consultant. He is currently implementing a software in the client side.Someone is trying to illegally try to take the source code. We don’t mind giving this to them but they have to pay us.So now I want to now is there anywayhe can keep a log of files that are accessed from his computer and also prevent anyone from seeing those files.Enabling those files as hidden doesn’t seem to help. Also this computer has a 98 os. So it would be nice if anyone could give me a practical solution for this.