I noticed that Plausible claims to measure traffic without being able to persistently identify users, but https://plausible.io/data-policy states that they store the following:

   hash(daily_salt + website_domain + ip_address + user_agent)

There are optimizations that can help brute-force the enumeration of customer domains, browser UAs, and IP addresses (e.g. in some cases you could enumerate only residential ISPs).

Update: I mis-interpreted "rotating salt" to mean something that could be re-computed on Plausible's backend. It appears that the salt is random[1] and generated on the client-side, which makes this hash much more secure.

1. https://github.com/plausible/analytics/blob/master/lib/plaus...