Need to block url in all browsers

I'm wrinting a small program and one of the feature is to block some urls when the user try to go on the web browser.

So I would like to know where can I look for information about how can I do this.

Thank you

Enter the addresse's in the HOSTS file

but the problem is that some users have different leves, and they will be able to see some websites that others cannot.

So I would have to rewrite the host files everytime a users login in to the computer? :confused:

dglienna solution's is very a pragmatic one. Other solutions probably need lots of development, for instance writing a web or socks proxy with user auth etc.

Maybe you can find a free web proxy that supports Proxy-Authorization on localhost with NTLM auth... (with url blocking support as well of course).

Buy a Firewall appliance for a business. That's the only way to make sure. Even with hosts file, people can still bypass it if they know how. You'd have a password to bypass the firewall, but, could also have many levels of authentication.

Use this server, it will allow you any kind of user access customization you want. Basically it's a proxy server.
http://www.microsoft.com/isaserver/default.mspx