What is "NDIS Filtering"?

Got this message in my NIS 2009 History Log yesterday (Feb. 27, 2010).

 

"NDIS Filtering is enabled."

This was the *very first* entry in the Log, for start-up that day.

 

To my knowledge, I've never gotten this message before -- nor since.

 

Cannot find anything on it, with NIS Help ("No Topics Found").  And, virtually nothing on the Forum, here, either.

 

Web info is quite confusing to my techno-weak brain.

 

Any help appreciated.

 

Robby