We have included webhttrack in our alternative firmware for NAS (lacie and
Philips). 
The downloaded files permissions is set 644 by default but this point causes
issues with our firmware because :
The firmware doesn't manage the accesses for the remote user at the files
level (all files created by the users have permissions 666) but at the shares
level using samba or ftp severs...

Of course, for a safety rule, the remote users don't have a valid shell and
they can't run directly htsserver (which it's run by the root user). So the
users can't delete the downloaded files with these settings.

So could confirm me if I change in htsglobal.h, the following lines
(387-388):
#define HTS_ACCESS_FILE (S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH)
#define HTS_ACCESS_FOLDER
(S_IRUSR|S_IWUSR|S_IXUSR|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH)
like this :
#define HTS_ACCESS_FILE (S_IRUSR|S_IWUSR|S_IRGRP|S_IWGRP|S_IROTH|S_IWOTH)
#define HTS_ACCESS_FOLDER
(S_IRUSR|S_IWUSR|S_IXUSR|S_IRGRP|S_IWGRP|S_IXGRP|S_IROTH|S_IWOTH|S_IXOTH)
The downloaded files permissions will be set 666 ?
Note : about translation files, they contains several single quotes and then
the text isn't properly displayed (truncated at the first quote). So, in the
text file, you should used the html encodage : "’" ;-)