You got hit with some sort of Adware. YOU must have approved it. No way it could have been installed otherwise. You got tricked into it. They're pretty good at it these days.
The way to help with that sort of thing is to make sure you're never signed in to your computer as an admin user. When you are, any little piece of software can run without further approval and install junk like that (but you still would have had to say OK or Yes or something somewhere.)
If you're signed in as a regular user instead of an admin, then when that sort of thing happens it'll bring up a username/password prompt because you need admin rights to install new software on the computer. If/when you see something like that pop up, but you know you're not actually trying to install anything or configure any system settings, then you can just close it and the adware can't install itself.
If you've already got the adware it can be a bitch to get rid of. You can try the adware removers but they don't always work very well. Depending on how bad it is you may just need to backup, wipe the machine, and re-install everything. It's a bitch, but then you can set your user accounts up the way I mentioned and you'll never have this problem again unless you really screw up and even type in your admin un/pw when the adware installer asks for it...which some people do because they can be pretty sneaky about tricking you into it. You just gotta be careful.
Anybody who tells you to get a Mac to solve this problem is showing their ignorance. Even if you're on a Mac the same shit can happen, and it does. You just don't hear about nearly as much because they're still only holding a small fraction of the user base for desktop computers and laptops. The more popular OSX gets the more vulnerable you'll be, and all these people who are training each other not to worry about AV or Spyware/Adware on Macs will be screwed eventually.
By the way, if it wasn't for the "hacker type" people you wouldn't be able to watch those streams in the first place, so I gotta say it really makes me laugh to see somebody thriving on the technology and the intelligence of these people, and then blaming their own ignorance on them at the same time.
The "hackers" aren't even the ones doing this sort of thing. It's the script kiddies who are just downloading little apps and releasing them. Most of them don't even know how it works, but if they get thousands of people to install it they'll make quite a bit of money "solving" the problem for people.