How does one even hack a Instagram account? Or get Hacked?

I'm not asking on how to hack someone, i'm just wondering how do they do it and how does someone even get their instagram hacked. Its an iphone app, I don't think you can have viruses on iphones like a computer gets, can you? But i'm just a little bit worried. I have 17k followers, i know that's not a lot to some but for some that's a lot but one of my pictures recently made it to the popular pages and i've been getting a hell load of new visitors on my page. I'm a little paranoid you can say but its just because i've had friends thats had 36k, 50k get hacked, and instagram never does anything about it.but, Like how? I know they have instagram online now, so its probably done online but i don't know, i was just always curious about it. Also, they never gave any of their information away either, i just don't know.

Hacking such accounts occur mostly in these ways:
1. Brute-forcing your password (see link below) - not likely because of security policies in such sites
2. Guessing your password by doing reconnaissance on you
3. Hacking your email and use "forget password"
4. Grabbing a password on another internet account you have (maybe more exploitable site) and trying the same password in Instagram

Moreover, there ARE viruses on apple devices although it is less common.

In short, no need to panic, just be smart:
1. Use a unique password for instagram
2. Change passwords regulary - prefer changing password from your apple device, good chances for no keylogging exists
3. Use strong passwords (check password strength link below)
4. Protect your email account the same way you want to protect your Instagram account