What is pre-bid vs post-bid fraud protection?
Pre-bid protection evaluates an ad opportunity before the buyer bids and skips it if it looks fraudulent, unsafe or unviewable, so money is never spent. Post-bid protection measures impressions after they are bought, reporting invalid traffic for optimization, blocking the ad from rendering in some cases, and supplying evidence for refunds. Most serious buyers use both.
Pre-bid filtering runs inside or alongside a DSP, using data about the domain, app, device and IP in the bid request. It is fast and cheap but only sees what the request reveals, so disguised fraud can pass. Post-bid measurement uses a tag or SDK that runs with the ad, seeing far more: whether the ad rendered, was viewable, and how the device behaved.
The two feed each other. Post-bid findings update the pre-bid blocklists and segments, while pre-bid filtering keeps post-bid IVT rates low. A caution: a low post-bid IVT rate on a heavily pre-filtered campaign reflects filtering, not the underlying quality of the supply.