The CAPTCHA question

I'm pretty sure I'm going to be revealing my true computer ignorance with this blog, but I have some questions about this CAPTCHA stuff. I'm sure a lot of you have seen this. When there's an issue of privacy or something, you have to read this tilted and messed up-looking series of letters and numbers. Then you enter it in, and you're good to go.

Who exactly is this stopping? Am I to understand that hackers, despite their hacking skills and general computer know-how, cannot read slanted letters and numbers? Is that just a god-given skill to all of us non-hackers in the world? We finally figured out that the true downfall of hackers is that they can't decode letters or numbers if they're slanted or overlapping? Like I said, I'm sure I'm just dumb and there really is some entity hacking into sites that cannot type in letters that appear jumbled on a screen, but what is it? I've heard of "bots". Are these just robots going around hacking into random accounts that people have? And am I correct in understanding that these robots, then, can type in a series of regular, upright, and not overlapping numbers and letters? Who programs these robots? I think if I had a robot, it would be smart enough to read jumbled up letters and numbers. I mean, if we can program a robot to read regular numbers and letters, why can't it read them all slanted and stuff? Haven't we figured out a way around that yet? So many questions I have about this.

What's next? The computer will show you a picture of random things going on, and you have to enter in a short, expository essay about what's going on in the picture to prove you're human or non-hacker (hackers can't write, either)? Or it ask you what emotion you are feeling right now, and if you can honestly answer, you can pass, since these "bots" can't possibly experience human emotion?

Somebody please let me know. I'm a very curious and inquisitive young man with a thirst for knowledge.