[Ukv]

Castle.io's customers seem to include marketing platforms, and their listed use-cases include preventing account sharing and alt accounts. Can understand why a company would want to be able to uniquely identify users, but also from a user/privacy perspective it's something I'd very much like my browser/extensions to block.

[jgalt212]

Detecting account sharing is a tricky business. It's pretty easy to detect if one account is using two different machines. But it's quite hard to unambiguously say it's one person using both machines or two different people each using one machine each.