I've just started an experiment on my quad core CPU which seems to make
WinHTTrack pretty unusable (using 3.42-2, either the downloading will just
freeze in the middle of a mirror, or more likely WinHTTrack will just randomly
close itself in the middle of a mirror): I've used imagecfg to permanently
change the CPU affinity of winhttrack.exe so that it only uses one CPU core.
I've used the same trick on another program (RegCleaner) which is not
multi-core compatible (you can run the exe but no gui is shown, changing the
CPU affinity to one core fixes this problem), so I'm hopeful that this may fix
these issues. So far, it seems to have stopped the random closing of
WinHTTrack. I will continue to monitor for a while though (and if I'd known
that the main change to WinHTTrack was related to multi-core, I would have
done this months ago - thanks for that info William).

Chris