That's exactly not what happens with scrapers. Scrapers make millions of requests, yes. But each one of those requests produces an average (token-denominated) reward V'. There's no asymmetry at all: you're just adding a fixed cost to each reward, for both users and abusers.
That's before you even get to questions like "does the system actually work, or does a single solve get practically unbounded rewards".
There is: users solve the PoW once, scrappers solve it every time they rotate IP addresses. Some of them change their IP address on every request, so they keep solving the PoW over and over.
Which: I get! If it's your site, perform all the anger you want.
Anubis doesn't really help against this.
Even if you had to solve a L6 challenge for every request it's faster than the total RTT time of most servers. In other words not a meaningful barrier. And L6 is already a level which severely interferes with human usage of a site.
a $5000 ASIC-based device can hash SHA256 at 200TH/s or more.
If the source IP was an issue, you could do it other ways: for example, make the cookie rotate on every access, and insist there is a single stream of accesses.
You say “they” as if all scrapers are a monolithic group with the same constraints and goals. Part of the problem is the massive diversity.
And yet many report it works, at least for now, and the excess load due to scraping activity falls precipitously when Anubis or similar solutions are used. Maybe once this sort of challenge is used almost everywhere we'll see concerted attempts to get around it, but for now it is easier for them to just move on to another target.
> a $5000 ASIC-based device can hash SHA256 at 200TH/s or more
Peanuts for the big players, but many (almost all?) running smaller scale scraping operations are going to find $5000 rather prohibitive, and they are unlikely to be able to integrate it as they are probably running a “stock” scraper that they didn't write themselves.
Not sure why anyone would characterize these scrapers im general as all being fly-by-night operations that don’t have two cents to scrape together.
If they are so stupid an idea that they could never work, why do they seem to having the desired effect?
If you've seen anyone post a comparison of crawl rate versus difficulty, I'd love to see it. There's probably some difference but I want to know how much of the overall effect it is.
I wonder if AI might be able to come up with new PoW algorithms in a nightly CI job so every day is a different puzzle...
My earlier idea was to imagine that each day Anubis picks an entirely different problem-class. Ex: one day it is Sha256, the next it is prime factorization, the next it is twin-prime-finding, the next it is cracking elliptic curves, the next it is some kind of sorting / information theory problem...
All with the goal of adapting constantly so that scrapers have a harder time optimizing for the PoW problem (i.e. with Sha256 ASICs)