end users all have internet access

ok, we have a winnt4 sp6 network. we have set up our network so that only a few people can access the internet. we have assigned them to a group called "internet group". but instead of only those few people being able to access the internet everyone can. so somewhere a setting was changed somehow and now everyone can access the internet. can anyone tell me how to fix this without having to go to each and every pc individually to set it not to have internet access. please this is crucial!!!