Fraud & invalid traffic · also called Browser hijacking, Search redirect malware
Search hijacking (browser hijacker)
Search hijacking is when unwanted software changes a browser's search engine, home page or results so the user's searches are diverted to pages that earn someone ad money.
A browser hijacker usually arrives bundled with a free download or as an extension that asks for more permissions than it needs. Once installed, it switches the default search engine or new-tab page, or redirects searches through a different results page. The user keeps searching as normal, but each search now passes through a page carrying a monetised search feed.
This is the dark side of a legitimate model. Browser extension search monetisation and default search deals are lawful when the user knowingly agrees to the change. Hijacking is the same plumbing without honest consent. Google's AFS policies do not allow its search code inside toolbars or browser extensions, and Google Ads' unwanted software policy targets programs that are deceptive, hard to remove or that hide what installing them will do.
Warning signs for a feed owner include searches arriving without a visible search box page, users who never chose the site, bursts of navigational queries (people trying to reach a website they already know) and complaints about a search engine "that keeps coming back".
The traffic is real people, so it can look clean, but it is treated as invalid because the consent is missing.
Think of it like this
It is someone secretly re-routing your phone so every call to directory enquiries goes to their own premium-rate line first.
Related terms
Adware
Adware is software on a user's device that shows or injects extra ads, opens pages or triggers searches the user did not ask for, to earn money for its maker.
Browser extension search monetisation
Browser extension search monetisation is earning search ad revenue from an extension that sets the user's default search, homepage or new tab page to a monetised search engine.
Default search deal
A default search deal is an agreement in which a search engine pays a browser, phone maker or app to be its pre-set search engine.
Malvertising
Malvertising is the use of online ads to spread malware, scams or forced redirects, so that simply viewing or clicking an ad harms the user.
Query fraud (fake search queries)
Query fraud is sending a search feed searches that no real person chose to make, in order to trigger valuable ads.
AFS program policies
AFS program policies are Google's rules for anyone showing its search ads on their own site, covering where queries come from, how ads are placed and what traffic is acceptable.
Sources: Google AdSense Help: AdSense for Search (AFS) policies, Google Advertising Policies: Abusing the ad network