UltraVNC should have the ability to filter big blocks of IP address ranges.
For example I live in belgium, I want to only accept connections from Belgium.
UltraVNC.ini does have Authhosts. But its not designed for doing partial IP address ranges.
Looking at the first range:
You could say
which would include that range, but much more.
UltraVNC needs a feature to be able to say
so only that range from 128 to 159 is included.