To sneak a peak at an opponent's screen, when competing in a multi-player, online environment, e.g. Call of Duty, in order to find out where they are so you can go shoot them. Screenhackers are the subject of much finger-pointing and deriding upon discovery.
John: "You're looking at my screen you cheating son of a wh*re"
Fred: "No I didn't, I was just checking my watch"
John: "I so caught you screenhacking!"
Fred: "No I didn't, I was just checking my watch"
John: "I so caught you screenhacking!"
by Pukezilla January 8, 2011
Get the Screenhackmug.