Thanks William Roeder. 
Excelent explanation.

As well as, I could research that httrack create a interesting files inside
hts-cache:
- doit
- new.lst
- new
- new.zip

I understand all this generated files by httrack. I don't only understand the
folder new.zip.

With the new.lst file I can see if the downloaded content was
added/updated/untouched

But what is new.zip?
Anyway, httrack is good web spider.

Ivan