In what cases will HTTP_REFERER be empty

Question

I know it\'s possible to get an empty HTTP_REFERER. Under what circumstances does this happen? If I get an empty one, does it always mean that the user changed it? Is gettin

Answer 1

It will/may be empty when the enduser

• entered the site URL in browser address bar itself.
• visited the site by a browser-maintained bookmark.
• visited the site as first page in the window/tab.
• clicked a link in an external application.
• switched from a https URL to a http URL.
• switched from a https URL to a different https URL.
• has security software installed (antivirus/firewall/etc) which strips the referrer from all requests.
• is behind a proxy which strips the referrer from all requests.
• visited the site programmatically (like, curl) without setting the referrer header (searchbots!).