Hacking is altering something in order to make it work in a way not originally intended.
In Minecraft, hacking refers to using a memory editor in order to alter the variables which the Minecraft java application is storing on your computer. This allows you access to blocks not usually available.
Legality
It should be noted that hacking is only appropriate in single player mode, and attempting it on a multiplayer server will result in the software kicking you from the room.
Note that some software such as wrappers might not kick you. Alas some custom servers will not kick people for these hacks either.
Method
- Pull out Cheat engine or another memory editor.
- From the PROCESSES List, select 'java.exe' (Normally found at the bottom)
- In minecraft, make sure you have the first block in your UI as stone.
- Scan for the exact value 1
- Go to minecraft and change the first block in the UI to cobblestone.
- Scan for the exact value 4
- Go to minecraft and change the first block back to stone
- Repeat step 4
- This should yield one or two adresses. Pick one (or both) and change the value to one of the following material locations given underneath.
Block memory locations
See here for a list of block values to search for.
Any selections above the highest block number will freeze your game due to the fact that there are no blocks to fill the slots for those numbers yet.
Consequences
Trying to do this will result you in getting banned/kick/ipbanned in multiplayer servers, though the server will know when you're cheating/hacking. It'll say "Cheat detected: Tile type" and will reset everything back to normal, so it only works in Single player.