[seri4l]

I apologize for the double negative. What I meant is that hashing doesn't improve privacy because if you know the hash and the hashing function it's easy to build a hashmap of all the possible IPv4s (around 3.5B). Unless the hash uses some sort of expensive key derivation function, but that doesn't scale.

[GordonS]

You could simply salt the hash, though you'd need to treat the salt as a secret.

Alternatively, you could use a new salt every day, which would only allow you to track an individual for a 24 hour period (likely enough for many).