That's not hacking -- it's social engineering. Your mods need a swift kick in the pants.
The only way to "disable" this would be to hide it from that usergroup. But any vB user with common sense would be able to manually enter the URL instead. This is a core function, so I don't think it could be disabled easily, or at all.
Most SQL injections are easily thwarted by blocking access to key folders, using unique database settings (prefix), and running mod_security (Linux) or UrlScan (Windows) with settings aimed at squashing long scripted URLs (GET/POST commands).
You can also lock users in the vB config, so their info cannot be changed via the admin panel.
Everything you experienced was avoidable.