[Mobhack]

In secure PBEM, each player has to keep thier turns in complete lockstep and ensure they complete thier turns properly - not sending an incompleted turn to the opponent for example. They also have to reserve the slot as mentioned above with no swapping games in and trying to share a slot with say 2 opponents simultneously, though that is usually seen users who have the demo game.

There are lots of ways that secured mode PBEM can fail, usually they relate to player turn handling.

If it is a friendly game with an opponent you trust then regular mode PBEM is much more forgiving of user errors and quite frankly, I would only ever use secure mode for a full competition style game. (It was requested back in MSDOS days by guys who played ladder type competitions).