As someone who has just had their entire website stolen by somebody using
HTTrack, using in excess of 50MB of my bandwidth, I was a little disappointed
to see no mention on the HTTrack website on how I can ban the HTTrack spider
from my site using robots.txt. 

Can you please point me to a section of your site where you clearly and
unambiguously document how I might achieve this? 

If you have not documented how I can identify and ban your spider can your
please create one and link to it so it is easily findable.

If you create tools like these you have a responsibility to allow webmasters
to control access to their site. I do appreciate that you are not responsible
for the errant behaviour of your users. You are responsible for implementing a
spider that follows accepted spider etiquette and to document said behaviour.

Kind regards,

Jack