If the network there is anywhere as disorginized as in my company, every proxy/firewall is governed by different rules ACL'd in different ways so even if the proxy were detected by WPAD, the user would not get out. I did not setup WPAD for the convenience of visiting users becase my rule base would not let them out anyway. I set up WPAD so that MY users would not have to change their settings when they take their laptops home or on the road. If they connect at the Corporate offices or at another division and need internet access, it is not my problem since the solution is out of my control.
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Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.