I've been working this today trying to track who is set up for our proxy and bounce it against who is actually authorized.
For all Win OS's I'm using:
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings\ProxyEnable and logging it by Workstation-username to segregate the profile settings.

Why not just set the above key to 0 to disable their access? You could also delete the ProxyServer value(s) for good measure.

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[email=glenn.deans@sea.siemens.com]~Glenn[/email]

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~Glenn

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Deadlines take their toll.
Please have exact change.