Cloudflare has a privacy policy https://developers.cloudflare.com/1.1.1.1/privacy/public-dns...

Obviously, for Thai users this is a reasonable option, but I would understand why American users would not want to use Cloudflare, Google or even Quad9, as these are all US-based.

The netflow data from cloudflare, which is 0.05% of all traffic, is retained for 60 days according do the compliance report. 8.3B log entries is a lot, but I suspect that given how large market share cloudflare has, 0.05% over 60 days is also not a small data set. My intuition with probability calculus make me suspect that given normal internet usage over 60 days, a person is more likely than not to end up in cloudflares netflow log.

> a person is more likely than not to end up in cloudflares netflow log.

They are, but because this is all Cloudflare's 1.1.1.1 service does, that log only tells you that the IP address used Cloudflare's service.

So whereas this Thai data more or less says e.g. You watched Netflix between 18:40 and 19:26 and then again 21:33 to 22:09 the Cloudflare data says you own a device that uses Cloudflare's 1.1.1.1 DNS service. Maybe you can try to do some kind of activity estimate e.g. me idly browsing random web sites probably causes more DNS queries versus a SmartTV just periodically doing auto-updates when I'm asleep, but the 2000:1 dilution would make that more unreliable.

It isn't strictly nothing but it's damn close.

If the attacker also have access to the anonymized data set which is stored for 25hrs they should be able to deanonymize quite a bit of the data by just comparing time stamps and finding patterns.

It is much better than just having normal logs laying around, and since the data is split in two data set, there is a possibility that having access to one does not automatic result in having access to the other. The dilution is also helpful, through I am uncertain to the extent given the amount of traffic generated.

Is a privacy policy worth anything? Genuinely wondering, can they be sued, etc, if they violate it and claim "Oops, we made a mistake and our data got leaked".

For example Facebook probably said they would keep your data secure, but their system to prevent abuse from 3rd party "Quiz" developers was "Developer, by clicking here you agree not to abuse the data you can access."...

I thought quad9 was UK based?

Bottom of quad9.net says:

HQ

1442 A Walnut Street

Suite 501

Berkeley CA 94709

Aha, figured out I was confused because I read about their membership in the Global Cyber Alliance which includes members such as the London Police and the NYPD.

Bonus if you are interested: forum thread where Quad9's director of the board comments about DNS are surprisingly informational.

https://www.snbforums.com/threads/cloud9-dns.56918/

Could be interesting to use a list of DoH servers and pick one at random for each DNS query.

dnscrypt-proxy can do that for you, downside slow DNS server means slow DNS responce time