File hosting sites make different tricks to ensure you was not hotlinking and show you advertisement and perhaps counter. There can be
- simple analysis of HTTP Referrer field in the request
- setting and checking session-unique cookies
- having HTTP Forms with hidden one-time values, and Download button would be not the link but the form's Submit action.
- generating one-time hashed URL, and encoding different parameters like your IP and your browser name into it
- maybe more
Tools like USDownloader and JDownloader makes a lot of attempts to circumvent it.
While zippyshare seems to be more liberal, it still cannot afford hotlinking and should implement at least some measures of self-defense. When analysing traffic - start with absolutely fresh browser loading zippyshare page for the 1st time in its life and check it all.
As i re-load the page few times i see that the number "604061" is different and link keep changing time and again after each reload. You probably have to load the page, parse the link, set the HTTP referer and only then download the file.
You do not show the HTTP traffic logs so it is hard to tell for sure.