Yeah, I was also just notified of this
mscorlib.ni.dll when my Avast was updated today.
The file was moved to the Avast virus chest.
Avast told me it had originated in "Bitmeter" a network traffic monitor system from
http://codebox.org.uk which I had installed a few days ago.
AFAIK, the Bitmeter still runs satisfactorily on my system...
-Tony King
aqk.ca