Tavis Ormandy called this, about Anubis, almost exactly a year ago:
https://news.ycombinator.com/item?id=44962529
It never really cohered as a solution. High-powered scrapers are better equipped to handle proof-of-work challenges than end users. Proof of work makes sense for a password hash, where any one guess at a password provides zero marginal utility. But every request from a scraper is productive to the scraper.
If you want to argue that there's excessive enthusiasm about anubis, which is neither a permanent solution nor a solution against all bots run for all purposes (some bot authors are cleverer than others, and you don't have to block everything, just enough to reduce resource use to tolerable levels)... fine.
However, the refrain from naysayers isn't that there's too much enthusiasm. It's that anubis doesn't make sense as a theoretical barrier against bots. Who cares as long as it works empirically, even briefly? Are you suggesting people let their sites continue to be degraded or unusable until they find a better solution, even though PoW challenges can improve the situation today?
Not everyone has the luxury of writing their own web app designed to handle massive bot traffic at minimal cost, gutting functionality to meet that requirement if necessary.
I noticed a couple of weeks ago that 1-2 orders of magnitude more bots were getting past anubis challenges. However, it would be incorrect to conclude that it's doing nothing and now worthless aside from heating up visitors' cpus. If I turn it off, I see >2x bots.
The next salvo in the war of attrition will probably be when anubis switches to wasm hashx, which the author suggested, in previous HN threads, is on the roadmap.
If bots quickly adapt (Claude vibe-coded JIT wasm-to-native-transpiler for hashx challenge algorithms?), that may be the end of anubis and efforts like it. If they don't, I expect more HN threads with people complaining that such compiler efforts are possible and therefore PoW-gated sites are doing it wrong... even if those sites stay usable.
If you just want to block the bottom of the barrel scrapers you don't need to do any proof of work. It's overkill and wastes user's times for such a purpose.
I'm not moralizing. The sites running Anubis are owned by people who like Anubis and are fully within their rights to run Anubis. I don't care how enthusiastic they are about it. It's their call.
I'm just saying, it's bad computer science.
I get what you're saying, but I think that in the abstract "here's this thing you can do to cut the annoying traffic down to 1/3rd its previous level" (with the obvious issues to legitimate users of course) feels like a nice thing to have in this current moment!
If you were dealing with a DoS like this and had an option that cut the annoying traffic in half in a fairly deterministic way, that sounds like a decent thing to do operationally in the moment right?
You're arguing worst-case, and people running anubis are saying it dramatically helps in their experience, because they're not getting too many of the sorts of bots that people like you and Tavis (correctly) argue are theoretically possible. So the argument that it's "bad CS" falls flat.
A better, perhaps the best, argument is that a worse bot mix might appear tomorrow, so anubis should be used as a runway for a better solution, and not as a solution in itself. If only everyone with a website had the desire (or AI tokens) to implement their own better solution. In some cases even desire or a lot of tokens isn't enough. I mean, you think kernel.org folks haven't put some serious thought into it? And yet, as HN argues about it, there's kernel.org running anubis at difficulty 5.
I don't know what you mean by "the best argument". My entire argument is that it's bad CS. I'm not trying to convince people not to run Anubis. If anything, I'm trying to convince Anubis to use better computer science. That would make more people run it! But even that's just a faint subsidiary goal; the real goal, as someone who works in this field and has designed proof-of-work antiabuse systems before, is just to add clarity about what can and can't work and why.
I too would love anubis to use better CS, if available. Perhaps you have some ideas for @xena, instead of just letting anubis continue on the trajectory of iterating its PoW approach?
Same here. But of course and as expected; 5 hours later, the GP comment offers no proper solutions for this "better computer science" they speak of.
It shows they really don't care and they are just rage-baiting readers in their weekly grumpiness without any suggestions.
Unless they come up with said "solution", they can completely ignored in their complaints.
I had a fairly long conversation with Xe privately about this and didn't feel the need to repeat it here, especially since (as the search box will tell you) I've already talked about this before. But, do go on.
I looked at your comments and there's a bunch saying that Anubis is bad CS but none I could find saying what, exactly, you want Anubis to do instead. You sure are posting a lot about how it's bad, though.
It is interesting, this particular user seems extremely active in this thread. I'm not sure if they have a bone to pick with Anubis in particular or some other reason for disliking the software so much, but to me it does seem overzealous. Regardless of if it's "bad computer science" or what, Anubis works quite well and is easy to customise to target it to specific botnets, as I've done. And this is coming from someone trying to develop her own non-PoW anti-scraper system.
You might want to note that "this particular user" is "extremely active" on this website.
(Nothing against it, I'm always happy to hear what Thomas has to say)
We are not asking you to repeat the full conversation here. We just want the actual solution that was discussed.
So could you give a short elaboration on what was this "better computer science" solution that you came up with in your discussion?
Which part of computer science is about getting DDoSed by billionaires who are above the law?
Where on Earth do people get the belief that:
- It's the SOTA companies doing it?
- Scrapers are doing it for training data?
Those are two assumptions I see in posts and threads around Anubis, that are taken at faith, and never once substantiated.
Because Anthropic already admitted it? [0]
[0] https://www.ft.com/content/07611b74-3d69-4579-9089-f2fc2af61...
It says "accused of"
What's your alternative hypothesis?
> It's the SOTA companies doing it?
There are more than just the American top dogs (OAI, Anthropic, SpaceX, Facebook)... especially the Chinese government with all its infinite cash resources and next to zero ethical constraints.
I don't trust the US top dogs at all, but I think the fear of discovery alone would lead them to not use "residential proxy" services. Non-US/EU entities however... who cares?
Why would they directly use a proxy service? I'd just launder the data scraping through some third party company that I could slough off if it ever turned into a news story. Not that anything would happen to them if they directly used these services anyway.
I disagree. The kernel finds it effective - 66% of scrapers are turned away directly.
The scraper problem now is fleets of residential proxy devices - often things like smart TVs, phones, and browsers with some “proxy SDK” installed as part of an app’s monetization scheme. They make a couple of requests to a site - just enough to fly under the radar - and move on to a different site.
If each new site they hit forces them to solve a proof-of-work, that’s a meaningful dent in their scraping performance. Many of these boxes may not even have the spare CPU power to efficiently solve so many proofs of work - and anything that makes an owner notice their device is running slow is something that could meaningfully impede adoption of these SDKs, or force the operators to choose between minimizing performance impact or scraping more sites.
It's weird to believe data center based, Internet-scale scraping operations will be less able to allocate compute to proof-of-work challenges than individual users. This is design problem with things like Anubis: proof-of-work depends on a cost asymmetry between attacker and defender. But in scraping, both legitimate users and scrapers get the same value out of a transaction.
And yet, in practice, it's true. I was getting about 600K requests to my Forgejo server a day from crawlers making idiotic queries: https://honeypot.net/2025/12/22/i-read-yann-espositos-blog.h...
I just checked, and these many months later after installing Anubis, I'm getting about 14K requests per day. It's unreasonably effective at cutting crawler abuse. It should not be able to reduce my traffic by 98%, and yet in practice that's exactly what it's doing.
I think that the most abusive scrapers are operated by people who absolutely suck at programming. If they didn't, they wouldn't be crawling every permutation of "show me the git blame for every file in this repo for every commit in its history". Were they actually competent, they'd be investing in smarts such that they weren't crawling a web frontend to get that information.
Have you compared against adding a JavaScript requirement with no proof of work?
Yes. That helped, but not nearly so much.
For PoW to work, you don't need scrapers to have less compute than users, you only need their compute advantage to be less than the load-generation advantage they would otherwise have. And unlike legitimate users, scrapers aren't carefully picking the URLs they request, so the average value they get out of it is probably rather low. They have to make it up in volume.
The implication here is that the proxy fridge forwards the Anubis challenge to a dedicated rig controlled by the scraper who efficiently solves it and returns the answer.
That's still a notable step up in completely and resource investment for the crawler
See also how captchas continued being effective for years despite services like anti-captcha offering to solve them for you for a fifth of a cent each by farming the work out to India. It took advances in AI that made it viable to reliably solve them on-device to bring the end of the captcha
That's not a step up, that is how they work by default.
> Many of these boxes may not even have the spare CPU power ...
I don't think that's generally how these networks use residential exit proxies. There are at least a dozen well-developed frameworks out there for decoupling the crawler from the network exit point.
Most res proxy exits are just slinging bytes for clients using SOCKS, or another tunneling protocol.
If nothing else, a modern scraper will want better control over their TLS fingerprints, and you can't get that if you're depending on the on-device TLS libraries alone.
Why would they even run a browser engine on the devices they're hosted on?
All they need to do is forward traffic and launder its IP origin. They don't even need to be able to (and would actually be well advised not to) decrypt TLS streams.
> 66% of scrapers are turned away directly.
Until they discover this neat trick [1] and solve challenges orders of magnitudes more efficiently than legitimate users.
The game theory of Anubis is not sound. It makes fundamentally less sense than Captchas, and even those have been on the way out for a while.
[1] https://news.ycombinator.com/item?id=49500040
It doesn’t have to be fully sound, it’s there to provide _some_ degree of interim protection.
Evidently, it makes _enough_ of a difference for the people running it. Criticising it is just letting the perfect be the enemy of the good.
The alternative to Anubis isn’t “something better that isn’t being picked”, it’s “completely unprotected”, and the people criticising it for being imperfect could helpfully move the conversation forward by actively suggesting a concrete alternative.
Sure, but then you’re essentially just doing versions of the old “what is 2+2” text captchas with extra computational steps, so why not save yourself and your users those?
How s that measured? How do you count human users who have been turned away?
Yep, all security is about making attack more expensive than defense. If they have a farm of other people's devices, as alleged in the article, then it costs them less to calculate PoW than it costs ordinary users. Ordinary users have to sit there waiting, whereas bots are somebody else's problem.