It's an unfortunate part of Pokémon battles that some opt to cheat or gain unfair advantages, with official tournaments also falling victim. Unfortunately it's a blight now potentially affecting Pokémon X & Y, as details of a "Battle Analyser" tool are emerging.
The tool works by setting up a PC as a Wi-Fi hotspot for the games, accessing and displaying the online data; it does this for all online battles and shows an opponent's entire team, including the moves that they choose. It affects all battle modes and can allow the cheating player to react to information they have no right to see. Some have tested with friends to ascertain its accuracy, and though not providing 100% results it still provides a major advantage over honest players.
The post on NeoGaf provides social network details for prominent members of the Game Freak team. By spreading the word — and not links to the software itself — it's hoped that Game Freak will act to block the workaround, through encryption or any means possible.
Here's hoping a solution is found.