Whitelist
From Cship
Most Internet filters work with a blacklist, which means that access to all sites is allowed, except some special sites (well, sometimes there are a lot of exceptions...).
A whitelist works the other way around: Access to all sites is blocked, except some special ones. For a normal ISP it is almost impossible to offer - because the Internet is nearly worthless. The whitelist scheme is used for example by free Internet terminals that are sponsored by a company which allows users the free access to their e-commerce site. This filter scheme is the most difficult to circumvent.
Some time ago, there was a German ISP who had a completely toll free 0800 Dial-in number. Once you dialed in, you only could surf to amazon.de and about 10 more e-commerce sites. But you could also connect to the other customers of the same ISP. So somebody with a flatrate connected to both his normal ISP and the 0800 toll free ISP could set up a proxy. So all the users of the free ISP could use that proxy to connect to other sites.
