Some exploits i saw for 1.8

Hi, i created a 1.8.8 server but there are lots of posts in youtube and forums that show some exploits. I searched for them here but i didnt find anything.
Please tell me if this exploits still work for minecraft 1.8.8:

In this video someone show how to force-op with a sign ingame: https://youtu.be/_bmlyu_TtyA

Here you can see how to hide commands in book links so an if an admin click it he can op someone: https://www.youtube.com/watch?v=Z8umRki0p9g
This is for a sign that can crash a server: http://www.wizardhax.com/2015/06/27/minecraft-1-8-1-8-7-sign-hack-sign-crash-player-kicker-download/
I researched about this and seems that hacked clients can write anything in signs and books to crash the server, execute commands and scam people. Also seems that hacked clients can write commands in signs like /op and the server dont check if the player who write it or execute is is an op or have the permission to do it.
Thanks, im scared, i dont want to close my server