Two years ago, network infrastructure biz Cloudflare launched the 1.1.1.1 Public DNS Resolver, with the promise that internet users could use the service to surf the internet without being tracked - by Cloudflare at least.

The biz positioned itself as a speedier, privacy-focused alternative to Google Public DNS, which operates using the IPv4 address address 8.8.8.8 and also promises privacy despite Google's extensive online ad business. Other DNS providers plainly acknowledge they'll sell network traffic data.

Internet service providers generally offer a DNS resolution service so that when people's browsers, apps, and other software need to connect to a server by its human-friendly domain name, such as theregister.com, the DNS service will point towards the appropriate numeric network IP address for the server, such as 104.18.235.86.

Cloudflare contends that third-party services like its own can provide greater security and performance than an ISP-run offering, particularly if used in conjunction with a protocol such as DNS-over-HTTPS.

But since talk is cheap, Cloudflare went the extra mile to have its privacy claims verified by a neutral, third-party auditor: global professional services firm KPMG.

Now, after rather more time than Cloudflare expected, the results show that the biz has lived up to its commitment, apart from a minor router oversight. On Tuesday, Cloudflare plans to publish the results of its audit on its compliance page.

"Cloudflare's business has never been about targeted advertising or selling user data," said CEO Matthew Prince in a phone interview with The Register. "The interesting thing for us is it turned out to be a lot harder to find an auditor who could do this than we expected."

Prince said he thought the entire process would take six months. Instead, it took nearly two years because the accounting firms approached didn't have a playbook for this sort of technically-focused review of policy and practice. The actual audit took over three months to complete.

"It has made us better as an organization," said Prince, "but I also hope it makes people realize that we're committed to doing what we said we were going to do, which is not using this data in a way that threatens the privacy of individuals."

The audit did reveal one unanticipated finding. The company's routers were randomly capturing 0.05 per cent of all network traffic, including the IP address queries of 1.1.1.1 resolver users.

As CTO John Graham-Cumming explained in a blog post provided in advance to The Register, Cloudflare does this separately from its 1.1.1.1 service, retaining this fraction of traffic for a limited period of time for network troubleshooting and defending against denial of service attacks.

"If a specific IP address is flowing through one of our data centers a large number of times, then it is often associated with malicious requests or a botnet," said Graham-Cumming. "We need to keep that information to mitigate attacks against our network and to prevent our network from being used as an attack vector itself."

Graham-Cumming said this data is not linked to DNS queries and does not affect user privacy. Cloudflare has updated its published privacy commitments to clarify this practice. The most salient of these is a promise not to sell or share public resolver users' personal data with third parties or use that for ad targeting.

Cloudflare previously disclosed that APNIC, the organization that provided the 1.1.1.1 address to Cloudflare, has access to some DNS query data (but not the log of IP addresses of those making such queries) for research related to DNS operations.

"We've tried to design all of our products from the beginning that data held by us is a toxic asset," said Prince. ®

Full disclosure: The Register is a Cloudflare customer.