How to stop online line bots

I assume you've mistyped but you wouldn't want a puzzle that humans could not solve to try and get a bot to stop working, you would get people not playing then.

But also, for many many many years bots have been quite good at solving captcha's.

Because it's not very effective. Sites have used captchas for years. Fully automated bots aren't the big bot issue people are talking about on the traditional sites these days though. The bots you see mentioned operating on sites like WPN/ACR, Ignition and GG almost always have human operators present nowadays. They're still easily detectable by other means, but a captcha isn't going to prevent bots when a human operator is present.

yes, I put an extra "line" in the title and meant "puzzle that bots could not solve". Surely there must be some kind of activity that most bots can't get past. A lot of sites still use captchas or other puzzles so something must work.

so if it is easy to detect, why are there still bots?

Because some sites don't put the necessary resources into their site security efforts.

Why would a big site like ACR allow bots to run wild when so many people complain about them and it is easy eradicate them?

Because it's very very very profitable to run bots in an ecosystem.

They help increase gtd's of tournaments, they keep game activity windows wider, they don't quit because they don't lose.

They are unfortunately, very good for business. And very bad for the ecosystem.

That's why it's important to be picking ethical people to work with, in addition to finding beatable games.

I don't know what sites actually allow them to run wild other than some app clubs and some very small sites that most people have never heard of. Some sites just don't care or don't think it's worth it to spend on proper detection unless the talk of the issue hurts their bottom line. The people put in charge of policing this stuff often don't have the necessary knowledge and understanding of how to detect all of the bots if whatever automated detection algorithms they have in place don't identify the cheaters for them.

With the help of TylerRM, MTTDatabaseReview and some others, ACR/WPN has actually banned a lot of bots this year. It's still an ongoing process to identify them all and then hope that they get banned, but I think if they continue to be open to banning the ones these guys bring to their attention then ACR will have much less of a bot issue in the near future than they did in years past.