With what FREE software, can I use to record hackers, and then report them?

That's it! I am sick and tired of fighting left and right back and forth up and down all day long fighting HACKERS! When I say hackers I specifically mean people that play a game called Minecraft. And there are servers that you can play, and the one I love playing like crazy is also poisoned with hackers. So, I decided to take GREAT measures to get rid of them. The only way you can get rid of them is by record a clear 3-5 second video of them hacking with whatever and then report it on the servers webpage forum. But, for some reason when I record it with my camera it turns out that it has too much mega bites or something, so I guess I need a FREE harmless software that I can use to record my Minecraft screen. I tried one of them before, but it was crazy laggy, so I deleted that one. I need something good. Can you please help me? I'm trying my best to be the good guy, by getting rid of the bad guys.

Read more: With what FREE software, can I use to record hackers, and then report them?