I'm helping a neighbor to run a small e-commerce website with reviews. Review forms are being spammed by bots that get even through CAPTCHAs, and the owner needs to clean them up constantly. Without CAPTCHAs, it becomes unsustainable.

They don't get a lot of bots trying stolen credit cards, but mostly because they are pretty niche.

I can believe study's results on user interaction, but their "security analysis" section (6.2) is deeply flawed - it only looks at the best bots, and not at the average ones. Meanwhile, as many other people in this thread can attest, (1) most of the bots are not really sophisticated, and get stopped by CAPTCHa, (2) the defense does not have to be 100% efficient, as long as form spam goes from 100/day to 1/day, things are OK.

Of course authors really wanted to write their conclusion, so they just ignored all the practical considerations. It's really a shame on the part of paper's reviewers.