In a recent patch, Bethesda's Elder Scrolls Online quietly added a "marketing attribution program" called Red Shell to its desktop client.
According to the Red Shell FAQ, the program tracks:
" Red Shell is a software package used by game developers and publishers to help them measure the effectiveness of their marketing campaigns. It works by tying information from marketing campaigns to in-game play.... Red Shell tracks information about devices. We collect information including operating system, browser version number, IP address, screen resolution, and font profiles... We do not collect any personal information about gamers. We don't collect names, emails, or addresses. Our service basically says 'this computer clicked on a link from this YouTube video and the same computer played your game.' "
There's an ongoing concerted effort on the official ESO forums to find the best way to either block or opt-out of the spyware software for privacy reasons. The program also raises issues concerning Europe's new GDPR laws, as players are not given the explicit option or instructions to opt in or out of the program, though that might be covered by the game's privacy policy.
Since there has been no official response from ZeniMax Online Studios or Bethesda as of writing, players took the initiative to email Red Shell themselves for opt-out instructions, and have been trying to block the servers using the Hosts file.
Red Shell replied, and said they would be "working with Bethesda to determine how you can pull the Bethesda Account ID we need from you to implement the opt-out for ESO in particular".
Sources: Massively / ESO Forum Thread