[cpeterso]

Even without JavaScript or cookies, HTTP request headers can reveal a lot of unique entropy:

  * Browser
  * Browser version
  * OS
  * OS version
  * Machine architecture such as x86, x86-64, or ARM
  * User locale
  * IP address
  * DNT flag

Trackers can also tag clients with unique cookie-like ETag or Cache-Control values that clients will return in future HTTP requests.