FPS issues and weird game behaviour.

Ever since the newest patch came (maybe the one before too) i've been getting frequent fps drops. I play with 40 fps all the time which is bad enough but it drops down to 10ish even when nothing is happening.

I've also experience pretty weird things from my games and i'm paranoid that i have a Trojan on my pc. Game randomly alt tabbed out. Player from the enemy team was randomly muted, it popped up in the chat with "Player is now being muted." and i didn't do it, wasn't even looking at the player list with TAB. (Unless there is a hotkey for muting champions which i may have accidentally pressed).

EDIT: Another in game problem i faced recently was jinx auto attacking minions but wasnt facing them at all. (The character model was facing away from the minions but the minions were still losing health during the auto attack animations). This was during one of my low fps spikes.

EDIT 2: I've seen black pixels flying around the screen sometimes.