[cj]

With 3rd party cookies going away, a lot of companies are relying on ipv4 and ipv6 hashes to correlate users across sites with first party cookies.

In other words, if Giphy has your email and IP address, they can help companies like LinkedIn and other brokers de-anonymize IP addresses more accurately with higher percent accuracy.

ISPs could mitigate this by rotating IPs every week, but of course you typically get 1 IP and it rarely changes.

[_cenw]

> You typically get 1 IP and it rarely changes.

At least in Germany this is only somewhat true on fiber. Most cable/DSL has been on dynamic assignment forever, and some are even on CGNAT for IPv4 now.

IPs are shitty stable identifiers - and yet, before we got a static IP with our fiber provider, the neighbors YouTube recommendations leaked into our own.

[cj]

I noticed with LinkedIn they send 1 tracking request with a hash of your ipv4, then the request 302’s to a 2nd API that sends the ipv4 hash together with the ipv6 hash (along with your email if the advertiser provides it in the tracking code). My ISP is also dynamic assignment but it never changes, so basically it’s static.

It’s definitely not a good stable identifier. But when you combine enough signals like that (plus screen size, geo ip, ISP provider, etc..) you can get pretty close to being just as accurate (or even more accurate) compared to 3rd party cookies.

Even if your IP changes once a day, that might be enough to keep your profile connected if you use LinkedIn, Facebook, Giphy, etc on a daily basis. Another benefit of this over 3rd party cookies is easier cross-device tracking.

The whole phasing out of 3rd party cookies might be a net negative for privacy because it forces advertisers to send even more data to ad networks in the never ending pursuit of view/click to conversion attribution.

Without 3rd party cookies, the best way to track conversions is to give Google/Linkedin/etc your name/email/phone/mailing address so they can try to map your clicks to the conversion indirectly without cookies.

No 3rd party cookies = huge catalyst for data broker industry.