Could be better

it is a good way to pass time. Here are some suggestions to improve it.
Make the number of digits variable for the user to choose, and not just the preconfigured choices.
Allow doubles to increase the challenge. 566789 for example.
For higher skill levels, allow alpha characters, except i & o. AM59W2
I agree with other comments that a notepad would be good, or a dummy line to allow the player to insert good guesses.

Nyeent about Vault Breaker : Full & Free logic puzzle game, v2.2