Why don’t some clicks have a referring URL?

The referring URL identifies the address of the webpage that linked to the tracking URL.

The referring URL is information the visitors browser voluntarily provides. The visitors web browser does not have to provide the referring URL and there is no way to force the browser to provide it.

The following are reasons why a visitors web browser may not provide the referring URL:

• You are using a HTTP record link within a HTTPS page (The browser will only pass the referring URL from a HTTPS page to another HTTPS page.  There is a good discussion about it here )
• The referring URL has instructed the browser to not provide the referring URL.
• The web master is using a URL shortening service.  This could also cause the referring URL to be recorded as the URL of the shortening services rather than the affiliates site.
• The link was opened from an email.
• The user has configured their browser with strict privacy measures.
• The referring URL is an intranet site.