Hacks in starcraft generally are considered to ruin the game, and though they are considered "illegal" by blizzard, they do not enforce it on battle.net for starcraft.Because of that people are using hacks such as maphack,stackhack,stay alive hack, and drop hack.

Maphack-a hack that shows the entire map. this is generally undetectable and cannot be countered.The only way to counterract a maphacker is a multiple attack.Even with that tactic, it is highly unlikely that you will win unless you also maphack.

Stackhack-Stackhack is a hack that allows you to stack such buildings as hatcheries,photon cannons,and any building at all.Several ways to combat this are "allyalert",a multihack, and a stackhack detector.Stackhack works by removing the vision from the player, in essence adding the fog of war to the players map, and the game interperates that as the player has explored, and any buildings there have been destroyed.All the player then needs to do is select his probe,scv,drone (previously dubbed ctrl+1) and stack.It is relativly hard to do with Zerg, because every time you build you lose a drone.

Stay Alive Hack-A hack that just allows the player to stay alive even though his buildings and units are gone.This is just a nuisance because when he decides to leave he still gets a loss.

Drop Hack-Drop hack creates a substantial amount of lag, effectivly dropping the character to add a disconnect on his record, which generally doesnt matter to most people.

These are the basic hacks.