CNAME Cloaking
A technique where a site disguises third-party tracking requests as first-party using DNS aliases.
Browsers are increasingly hostile to third-party requests. To work around this, a site can create a subdomain like 'analytics.example.com' that points (via a CNAME DNS record) to a tracker provider's server. The browser sees a first-party request; the tracker still receives the data.
CNAME cloaking defeats simple URL-based blocking. Effective blockers respond by resolving DNS at filter time, by maintaining lists of known cloaking patterns, and by inspecting response content rather than only the request domain.