What is a hidden referrer or a generic referrer?

Referrer information is extremely useful in determining the source of traffic for your campaign.

However, some vendors are using techniques to hide the source of campaign impressions by removing referrer information (hidden referrers), or by replacing the URLs of referrers, usually with their own ad server addresses (generic referrers).

How did we do?

What is a good Quality score?

What is the difference between no referrer and other referrers (in the tracking point violations table)?