Hello Everyone! while this solution is really easy, it seems as though I haven't found this anywhere else. This process will COMPLETELY remove the Corruption/Crimson without doing it manually in-game. Some say these add a nice challenge to the game, but if you are like me and you just want to sit back and relax, then this is for you.
To start off, you need to download some software called Tedit. I will put the link here: http://www.binaryconstruct.com/downloads/ . If that doesn't work, then just look up Tedit downloads. Make sure to download the correct version corresponding to the correct version of Terraria. (Most likely the latest version will work) Once you have done that, extract the files and open up the Application from inside the folder you just extracted.
Now before we mess with the application, first we need to get the world set up. Make any type of world any size on any difficulty, and make sure to load into the world. (you can do this on existing worlds also, it doesn't matter). I would strongly suggest having one corrupted/hardmode world separate, because you need certain hardmode mobs and ores that you will not be able to obtain once you cleanse your world. If you want, in Tedit, you can actually set your world to become hardmode without having to defeat any of the bosses. If you want to do this, first exit the world, then load the world in Tedit (I will explain how to in just a second), then under World properties simply check the box where it says hardmode. Save it in the program then load up your world. Tada! I'm telling you this because if you want, you can then destroy some of the altars so you get the hardmode ores spawned into your world. That way you can have ores and still have a totally cleansed world.
Now back to where I was. Once you have loaded into your world, go ahead and exit now, and open up the application. Under the File tab at the top left, you will see the "open" option. Select that and it should take you to your list of worlds. If it doesn't, they are under Mydocuments/Mygames/Terraria/Worlds. Open up whatever world you are choosing and up should pop the image of your world. You can now change things like what bosses you have defeated, whether it's in hardmode or not, and many many other things. (If you want to change anything about your world, you have to be exited out from the world, and then you have to remember to save your changes before you load back into the world).
Now then, on the very bottom left there is a button called morph. What you want to do is click on that and under "morph to biome" make sure "purify" is selected. What this will do, is when you run your cursor over the Corruption/Crimson, it will replace any Corrupted blocks with stone, and leave all the ores/dirt/anything else in there. Make sure to make the size of the tool 200 x 200 and just slowly run your cursor over all of the corrupted land on your world. After you have run it over the whole world (Remember to run it over the whole world because if you broke demon altars a random piece of Corruption/Crimson will have spawned somewhere underground), then you can save it.
Now simply load back into your world and there you have it! A completely cleansed world where you will never have to worry about Crimson/Corruption again! There aren't any "side affects" that I know of, and it's pretty straight forward. If you have any questions, I will most likely be able to answer them. I've done this several times myself and even helped others do it. There are small things you need to know that I can answer if you ask them. Like how to get hardmode ores, or what if you break an altar after you cleanse everything, or even what to do if you go into hardmode after you have cleansed your world. I will answer these three things and if you have any more questions just let me know.
1. To get hardmode ores, you need to either go fishing and receive golden crates. (those will let you have hardmode ores), or you can do what I said above and break demon altars before you cleanse you world. The last method is simply having a secondary world you can get them from. (I highly suggest doing this because this also allows you to progress in the game if you need to fight specific biome mobs or anything like that). It's what I do
2. If you end up accidentally breaking an altar or something after you have cleansed your world. Simply just re-cleanse it by exiting the world and running the tool over your whole world.
3. If you defeat the wall of flesh, a V shaped structure of Corruption/Crimson/Hallow will form in your world. Again, just make sure to use the tool in Tedit and run it over your whole world.
If you end up missing any blocks of Corruption/Crimson, and they start to spread, it's really easy to contain them with this amazing tool. This is overall the easiest method that doesn't require you to do some major work and grinding to get it removed. While it is the easy way out, if you have a secondary world with Corruption/Crimson, it's really nice to have a completely clean world you can just sit back and relax and enjoy building.
Thank you all for reading, and feel free to add me on steam: Trojan_Death
