How is invalid traffic detected in search feeds?
In layers. Simple filters remove known bots and data-centre addresses. Device and browser checks look for automation and spoofing. Behaviour analysis examines timing, movement and click patterns. Statistical checks compare each source with normal rates. Finally, advertiser conversion data shows which sources produce clicks that never become customers. Checks run before the click, after it, and at month-end.
Pre-click filtering decides whether to show ads to a visitor at all. Post-click analysis reviews clicks afterwards and feeds refunds. Search engines do both, and their strongest signal is one publishers cannot see: whether clicks lead to an advertiser conversion.
Publishers and providers can run their own IVT detection to act earlier. Useful signals include data-center traffic, headless browser traces, mismatches between declared device and real behaviour found through device fingerprinting, impossible click speeds, and sources whose Ad CTR is far above normal. A sudden rise in click rate with no rise in conversions is the classic warning. Detection is never perfect, so it works best combined with strict sourcing.