There is no need to tell their ISP.  Their ISP may not be responding. 
Blocking the word "HTTrack" everywhere would be easier.

    I think I didn't make it clear.  I might be too polite to show my anger at
this event.  I was waked up by rings of the phone from IDC in Sunday midnight. 
Do you understand the feeling of being waked up in the Sunday midnight for
such a thing?  It's Sunday midnight, a time to sleep and rest to prepare the
whole week workdays.  Will this make you clearer about what I'm talking
about?
    I wonder what would happen if I'm out for some fun at that time?  Our
company might be facing refunds for the interuption of the contracted,
claimed-to-be-qualified web services now.  That means thousands in USD.  Are
you sir going to pay for that?  Or the so-called "abused user" in Myanmar? 
Spending months to find the guy in Myanmar and sue him for the refund?  Or
you?  I believe most of the lawers will give us the answer, "you".

    We ARE the content providers.  It's our mercy to provide content for
offline browsing for the convienence to the readers.  A non-threaded offline
browser, like wget, may take 1 day to grab a whole site, but this is still
faster, more convienent and more efficient than viewing pages and save them
one by one manually.  Then what are you asking for?  More?  Faster?  As fast
as a rocket?  What's so good of being such a greedy user?
    I have discussed this event with my boss.  In our point of view offline
browsers should never be threaded.  Threaded offline browser is itself an
abuse.  Some of our light-weighted servers even crash for continuously 4
simutanuous MySQL queries, and the user will never know.  And even if they
know they don't care since this does not hurt them at all!  This hurt us, the
free web content providers, not them.

    You are creating a tool for one end to get the benifit and the other end
to pay for it.  It's like providing guns to the teenagers and telling them not
to abuse it.  Please, for the God's sake, remove the threading and connect and
request one by one.  There is no need to be greedy.  This is still faster and
more efficient, without threating the poor content providers like us.