Just a few additional closing thoughts on this:

It turned out that I had a single classic asp helper script residing on the same virtual host as my DNN installation that I had forgotten was even here. It was this classic ASP script that was faulty, and was listed on Google where the url path was exploited by the SQLinjection worm. The SQL exploit managed to corrupt my DNN tables even though it didn't directly know of them. That is very creative.

This time, it turned out it was a QueryString URL exploit against .asp pages. Looking through my logs it is evident that my .aspx pages are also a target of several SQL injection attempts (both GET and POST attempts) so don't overlook the need for tightening and securing your web services.

Thanks again to the DNN folks who helped out with this, even though my DNN outage was just an unfortunate side effect of this exploit.