I’ll preface this post by saying I’m definitely not an advocate for using this hack, but if you find yourself getting knocked off by an invisible opponent, at least you’ll know what might be going on.

A lag switch is a device that causes a network disruption during online gameplay to the benefit of one of the players. As the video above shows, it can be made with a dollar’s worth of parts and very little technical proficiency. From the Wikipedia entry on online game cheating:

By attaching a physical device (called a lag switch) to a standard Ethernet cable, a player is able to disrupt updates/communication from the server with the intent of tricking the game server into continuing to accept client-side updates (which remain unimpeded). Since the client game-player is impeding the reception of information download, on the client game-player’s side the opponents will slow down or stop moving, allowing the client game-player to more easily shoot them, block them, out-race them, etc. From the other players’ perspectives, the person using the lag switch may appear to be teleporting, invincible, having delayed animations or fast-forwarded game play, or the player may simply find themselves losing to an invisible opponent.

Though I’m not a gamer, I found this cheat to be particularly interesting since it abuses the very mechanism that’s supposed to make gameplay fair and smooth for players with differing connection speeds. The hack essentially interrupts the Rx pair of the ethernet connection, while allowing the Tx pair to continue transmitting. The game is designed so that in a normal lagging network scenario you can shoot at other players in the location where your game client perceives them to be. Otherwise, you’d have to be predicting the future, aiming at where the other player will be seconds from now when their network packets finally arrive. Shut off only the Rx pair, and your game client can only interpolate the location of the other players; they effectively stop. With the Tx pair still active, your client is still able to send collision events to the server, making your opponent dead (and you a cheater).

I don’t think this is a new hack by any means, so chances are there are games that are affected, and many more that aren’t. Any regular gamers out there want to chime in on what games are most affected by this? Is the practice common? It seems like this would just about completely spoil an otherwise fun experience.

How to Make a Lag Switch
Wikipedia: Online Game Cheating