Those quizzes are hard. ;P
Maybe you should also make your lvls are better and more interesting like adding a race to the end of the lvl. The winner gets to answer first. Also, put in more eyecandy, more rewards, etc. Don't forget to give ppl coins so they can buy stuff for..er..I dunno. A very important thing is to make sure that the boxes are un-enterable after the game starts. Use a different tileset. Add a Hall of Fame. Enable a rating system for spectators. This should keep those hackers busy. ;P