Modded Minecraft

Hello. I really like using mods on Minecraft, since it really changes many things in the game, how everything works and it's simply limitless! Anyways, sometimes I go too deep while I'm searching for mods, and by that I mean dangerously deep. I was looking for some mods, and I think I went more than the 15th page of Google searching for mods. After some time, I find a link. It was something like http://www.k89.xyz/minecraft/mods/v84? I don't know, it didn't look as legit. Anyways, I really didn't care at that time and just downloaded the mod like nothing and completely forgot about putting it in Minecraft until the next day. I open the game up. The moment after I click on my world, the screen turns black with white bold text saying "Welcome!". It looked very amateurish, almost as if it was made in paint with the text tool. The world appears, but the chunks don't load, so I'm going to say that was a loading screen. The hotbar starts scrolling insanely by itself. I can't get any items. Around ten seconds pass and it stops. The inventory fills with cobblestone and more stacks of it fall onto the ground. I immediately clear my inventory and clean everything up and continue on playing. I look to see if there's something new in the mod, and I was right. There was an item called "Book and Quill 2". I open the book and quill and there's already text in it saying "Welcome to the v84 mod! Made by Z Press F6 to see your new, improved Minecraft!". Ehh, alright. I press F6 expecting an "improvement". A huge lag spike appears before the game crashes. Is the mod that big? Jesus! I open Minecraft up again and this time it works. I go back into my singleplayer world, same welcome/loading screen, but this time, the game is different. I'm trapped in adventure mode in a building which looks like a jail, and I can't do any commands. Z joins the game and appears right in front of my face, making me jump. His skin was strange. It's a normal Steve skin which just randomly has a red tophat on? I don't know how he got that red tophat, but I'll say it's really stupid-looking. I try speaking in chat, but nothing appears and there's a message telling me I broke rules? Which rules? I'm on a singleplayer world, god darn it! Anyways, I go to that website again and notice there's a full forum of it! I open the forums, and a link pops up leading me to the forums. Is that really necessary? Just make a hyperlink that immediately links to the forums. I click the link which was apparently http://www.forums.xyz. Yes, how original. I click on the forums and log in with my account. It loads... I'm on the forums now. I make a post asking for an answer to how I broke rules, and five seconds pass, I refresh the page and it's gone. "This page was terminated or no longer exists". I go back to Minecraft, and I'm in creative, no longer in the jail. I still can't speak and Z is still on. He starts speaking in chat.

 Why did you do this?

 Why did you do this to me?

 You will be punished for this.

I still can't speak, and I'm confused. I put up a sign saying "What did I do? I just downloaded a mod!". He speaks again.

 You already know, Marco.

...No I don't, and how do you know my name? I put that same sentence on the sign, expecting an answer. He doesn't speak. 5 minutes of dead silence.

Z left the game.

I go back to my Minecraft directories and move the mod back to my garbage bin. I create a new world and load it. Everything is fine... and then the Minecraft directories turn on by themselves. The mod is inside now. It minimizes back to the game and Z joins the game again. This time, he doesn't speak so I try speaking. It works.

 Who are you?

 Use signs to communicate if you're having trouble speaking.

Z doesn't put up a sign. He pulls out a sword and attempts killing me even though I'm in creative and he isn't. I /kill him and tell him to get off my singleplayer world.

 How did you get here anyways? Get out!

Z left the game once again.

...Something appears in my chat, though. There's no sign of who said it, it just appears in chat.

'''Goodbye, Marco. I know your address.'''

I try speaking in chat again.

 How do you know my name, and why are you saying goodbye?

The game closes by itself. I really don't know what happened then.

Three days later, I recieve a package.

'''I said I knew your address. Why don't you believe me?'''

-Z

Z proved to me that he knows my address. I'm scared. Is he a friend pulling a prank on me, or is he a hacker/serial killer? I really don't know, but I do know that I shouldn't play with mods anymore. Please, NEVER download anything that you don't know what can do unless someone can find out your address and potentially hurt you or even kill you. Take ca-=-36p2