Random "Hack Tool Detected"

OS: Windows 7 64-bit
Occurence: In middle of a game

Details:

For a few days now the game has run smoothly but just today, in the middle of games, a popup comes saying "Hack Tool Detected (1)(5.00)" or something like that. I have never hacked before and i was kinda surprised when this came up. When i clicked the okay button, it closed my crossfire game. I havent been able to play any games so far.