Services that are embedded in a third-party context will now see distinct IPs for each top-level domain that the user is visiting. This negatively impacts the ability to count the number of distinct users across a set of sites, and makes it easier to inflate impressions and ad clicks by having these same users engage on multiple sites.

Some attributes, such as GeoIP, may allow sites to validate observed regional distributions against what is expected.
We are keen to discuss any suggestions that could improve defensibility within our privacy objective of preventing scaled cross-site tracking.