On XP Pro SP3 I have a user account setup as limited, this means the user cannot install new programs, so far so good. I am trying to restrict Internet access using ZA Extreme Security but the block all internet activity is not working (I will sort out with ZA technical support next week).

Meanwhile what I can do is set individual programs to "kill" to stop them from working. However someone can get around this by using a browser that does not have to be installed such as Firefox portable.

What is the best way to stop any "unknown" (not installed) program from accessing the internet (without using block all internet activity)?