Request for Admin UID/PW Immediately After Login?

I just logged in to my system after restarting and immediately, before opening anything (other than Finder obviously), was presented with a request for the admin credentials (I was logged in to a user account), I think saying something about a change to my login preferences and/or login window, which didn't make a lot of sense to me.

Any idea what would cause this, or how to make sense of the logs to see what exactly prompted the request?

I installed Flash and Adium on this new machine this morning - would this have anything to do with it? I'm unaccustomed to getting the security prompt at unexpected times and now very nervous about whether this was malware, etc.