Why am I seeing "unknown" traffic sources

There are a number of reasons why the traffic source may be showing as "unknown", including the way the browser is handling redirects, users configuring their browser to not send referring information, traffic from secure (HTTPS) to non-secure (HTTP), etc. 

The most notorious of these is called a "Meta Refresh" which has commonly never passed on HTTP referrers within IE and Firefox.

The rule of thumb is that affiliates should prefer standard A links over JavaScript, and should prefer 301 or 302 redirects over meta refresh.

Below is a list of types of redirects and the browsers that do or do not support them.

STANDARD LINK

Chrome - OK

Safari - OK

FireFox - OK

JAVASCRIPT WINDOW.OPEN

Chrome - OK

Safari - OK

FireFox - OK

301 REDIRECT

Chrome - OK

Safari - OK

FireFox - OK

302 REDIRECT

Chrome - OK

Safari - OK

FireFox - OK

META REFRESH

Chrome - OK

Safari - OK

Firefox - No Referrer Sent