To change the default behavior, simply go to the preferences in Font Book and select the option that says install new fonts "for me only." Unfortunately, the current user can easily change this option prior to installing a font. IMO, Apple should make this option changeable only by an admin user.
[robg adds: On three machines I looked at, two of which had never run Font Book before, the install option was already set to "for me only." So the hint in this hint may not be necessary on your machine. The more interesting question to me is how big of a security hole is this? What can be hidden in a font file? Other than making life difficult by installing a corrupted font, are worse things possible? And since the 'attacker' will already have physical access and a login account, it seems there are much worse things that he/she could do in this case. Thoughts?]

