Default post order in thread display for unauthenticated users

[El Queso]

I've searched for quite awhile for something on this and can't find what I'm looking for. Admittedly I'm new at vBulletin programming - the answer may be relatively simple, but for a newby there is an overwhelming amount of information to sift through!

Is there a way to change the default order in which posts are displayed when displaying a thread to users who are not logged in?

The default order is earliest posts first. I have a large forum with threads that reach hundreds (some actually thousands) and go 'way back in time. When unauthenticated users are browsing the forum, I want them to see the latest posts in a thread first so they see the latest information.

I can't find any admin options that allow me to set this default for any but logged in users. I'm assuming I will have to either use a plugin/hook or do a hack, but I can't figure out what template, code file, hook and/or variable I need to look at to make this happen.