Fraud & invalid traffic · also called Referer spoofing, Fake referrer
Referrer spoofing
Referrer spoofing is faking the information that says which page a visitor came from, to make low-quality traffic appear to come from a trusted source.
When a browser moves from one page to another, it normally passes along a "referrer": the address of the page the visitor just left. Trackers, feed providers and fraud filters use it to understand where traffic originates.
Referrer spoofing replaces the true origin with a false one. Visits that really came from a pop-under network or a bot script arrive labelled as if from a search engine, a social app or a quality publisher. In search arbitrage this is used to slip unapproved traffic past traffic source approval, or to strip the referrer altogether so nobody can tell.
Signs include referrers that do not match the Click ID or UTM parameters on the same visit, a "social" visitor whose browser is not the app's in-app browser, large volumes with a blank referrer, and upstream pages that do not actually link to the lander.
Google's RSOC rules require parameters to be accurate and complete, and declaring a false upstream source or creative is itself a violation. Defence is cross-checking: compare the referrer with the paid click records from the traffic source and with on-page signals.
Think of it like this
It is a forged postmark on an envelope, so a letter posted from a back alley looks as if it came from head office.
Related terms
Domain spoofing
Domain spoofing is falsely claiming that traffic or ad space comes from a well-known, trusted website when it really comes from somewhere else.
Traffic laundering
Traffic laundering is passing low-quality or prohibited traffic through intermediate sites and redirects so it reaches a search feed looking clean and legitimate.
Traffic blending
Traffic blending is mixing cheap, low-quality or invalid traffic with good traffic so that the average looks acceptable and the bad part goes unnoticed.
Traffic source approval
Traffic source approval is a feed provider's sign-off that a particular place you buy visitors from is allowed to send traffic to its search feed.
Redirect
A redirect automatically forwards a browser from one web address to another, often passing through a tracking link that records the click along the way.
referrerAdCreative
referrerAdCreative is a Google AdSense for Search parameter in which a publisher must send the exact wording of the ad that brought a visitor to a related search page.
Sources: Google AdSense Help: Related search for your content pages, MRC Invalid Traffic Detection and Filtration Standards Addendum (June 2020 update)