Thanks for asking. First, our main focus is on making something more usable for people. We also think captchas are only part of the solution and should be employed with other things (rate limiting, keyword filtering, etc)

That being said, we don't just ignore security. There are a lot of captcha alternatives out there that survive on just obscurity, if they were widely adopted, they wouldn't take much to get around (like a slide to unlock captcha). We analyze mouse movement and other behavior, to avoid this.

To test our algorithms, we write our own bots to break our game (as well as working with the AI lab at the university of michigan) and use that data in our machine learning algorithms. We're always tweaking the bot to see how we can beat it and then looking for new features from the data that we can use.

The main point being, that as people do write bots, we can learn from that and incorporate it. We can also adjust the threshold. Some of our customers care much more about usability and just want a minimum level of protection, other's want the threshold a little higher and accept the risk that humans might fail more often.