Comment 1 for bug 1465205

All the levels from the Machines-vs-Machines level pack are proven to be doable on hard. I know 4 people in persons (excluding myself) that managed to do it. And there's a few more in the comments in the app store that claim having beaten the game.

I personally have not managed to win the Shoot-the-serifs level pack on hard. Michal Predotka might know if that has been tested/proven to work or not.