if i'm not wrong, using:
and the server will not be present in the list.
This is how you keep a server private. It's not what Elysium is talking about. He wants a filter setting that will hide anti-cheat required servers in the web page of the public server listings or the opposite, a list of all anti-cheat required servers. This would be selectable in the same way mods, game types and maps can be filtered.
I believe the combined filter is http://q2servers.com/?ac=3