Remember the old Mastermind board game, where you had to guess combinations of colours and were told various information about each guess, gradually deducing what the 'correct' combination was? Now apply the same idea to numbers and make the code the secret PIN for a bomb - and you've got the elegantly simple Defuse The Bomb, here free from the Nokia Store, with small on-screen banner ads.

Here's Defuse The Bomb in action:

In fairness, the bomb stuff is only window dressing - there are no explosions or ticking sound effects, and so on. But the core 'Mastermind'-style logic gameplay is as brain-stretching as ever, don't worry...

In fact, it's all rather well done - with an attractive interface. Guessing in 'expert' mode is almost impossible, unless I'm missing something or unless you're very lucky. Each digit can only be used once per code, which makes things a bit simpler, thankfully!

As with the original Mastermind colour puzzle, the point at which you move from 'let's try this complete guess' to no-holds-barred deduction is the fascination here. Constructing a 'guess' which is consistent with all previous guesses and scores provides a lot of brain exercise - even more so than the original game, arguably, since there are ten options per slot here (as opposed to six colours).

Recommended for you next train journey! 

You can download Defuse The Bomb for free from the Nokia Store here.