I did just this. Using a $2k a year database from a smaller provider that isn't maxmind, claude and I built a pretty slick ASN based categorization system. I can categorize an ASN as a residential IP, a service provider, a legit crawler/scraper, etc. For anything that is suspicious, I dynamically use turnstile to gate access to our service. Turns out there's no ISP for any VPN, they just contract with a shitload of mom and pop shady colocation services across the world.

We collect signals that help determine good vs bad networks. For example, large amounts of requests to .php endpoints, large amounts of empty accounts from the same /24 subnet, etc etc. All these signals let us automatically determine risk, and then put up a challenge. Authenticated users never see the challenge even if they are on a risky network (VPN 99.9% of the time), unless the network has been identified as 100% malicious, then it gets a full block.

Here's a small snapshot of the dashboard:

https://cos.ridewithgps.com/screenshots/6a7c54d0-12Aug26-358...

This was probably a total of 3-4 days of work, spread out over a couple months of iterative claude led hacking. I didn't know exactly what to build, but had some of the key architectural ideas in my head. Opus+Faable made easy work of it all, and ended up guiding some really slick improvements for performance.

I would say this has dropped about 20% of all traffic to our service, though it turns out turnstile is a massive target for bots, so replacing that with something custom is next on the list.