[from the carnival game which involves quickly and repeatedly hitting the heads of mechanical moles with a mallet as they pop up from their holes.] 1. The practice of repeatedly causing spammers' throwaway accounts and drop boxes to be terminated. 2. After sense 1 became established in the mid-1990s the term passed into more generalized use, and now is commonly found in such combinations as `whack-a-mole windows'; the obnoxious pop-up advertisement windows spawned in flocks when you surf to sites like Angelfire or Lycos.