Fighting curruption has some tactics which will be writed down here:
Going ahead the corruption and hallow a small place. Hallow can stop corruption and spread on the other side while it can be a way to stock up some pixie dust if you use holy water.
(The following tactic is used only if you want to stop monsters from spawning on the surface.) As corrupt monsters will spawn only from Ebonstone, Ebonsand or corrupt grass, you can hallow the surface using Holy Water and be sure to hit any thorns as thorns can spread corruption even if hallow is near.
(The fallowing tactic is used to make it easier fighting corruption.) This is a primitive and yet simple way of making this all easier: first close all the chasms with something un-corruptable, one block thick bridge over the chasm is enough.
(the following tactic is used only if you want to contain the corruption while being in pre-hardmode) Dig a three blocks wide underground trench under the corruption and make the blocks who are block 1 and 5 if count 1 is one up from player and 5 one down to be anything, but not mud, dirt, stone, sand, demonoid bricks or demonoide ore. and make the trench to be COMPLETELY under because one ebonsand or ebonstone can be (in this case) lethal.
Please write any other tactics:)