said by treichhart:well see I work for a local ISP and if there was a virus on your computer and its messing up are network we disable the user intill the virus as been fix and that anti-virus as to be to update before we can re-enable the service.
also on are wireless network say your package is 768kbps/256kbps and if you have p2p or virus on your compute we can turn down the service to 47.1kbps intill you get the problems fix.
The danger of throttling a user is, they will just blame you for the slowness and YOUR bad performance and switch to your competitor with their infested machine.