FIREWALL: Defender 001

There's always been a great link between what we can't see and what we don't understand. Trying to explain to my beloved parents why their PC freezes after they've opened up their 27th simultaneous application or how clicking on email attachments from dodgy Ugandan banks might not always be a good thing is no easy task. After all, what's a computer virus if you can't actually see it? What harm can something you never actually visibly encounter do?

In this way, FIREWALL: Defender 001 serves a unique and perhaps surprising purpose – one my parents could probably benefit from, if ever they were to stumble across Solus's world of worms, trojan horses, and phish. This isn't some kind of freaky genetic farm, but rather a stylised world of computer viruses. FIREWALL is a visual take on how these viruses attack computer systems and your goal is to build up a barrier of defences – or firewall – to block these attacks.

Defending is all about placement. Undisturbed, viruses attack from the top of the screen and head towards your base at the bottom. Their paths, however, can be altered. Depending on where you place your defences, viruses will skirt around the screen to evade them. If it sounds a bit like a game of Tower Defense, then you'd be right to assume the same strategic thinking applies here.

Successful tactics rely on flexibility. Initially, you're only able to place proxy blasters, which provide light defence. Stronger defences become available as you take down your enemy in greater numbers, though only the first two types – the proxy blasters and packet breakers – cause damage to all types of viruses. Two other types of defence offer more devastating attacks, but only to specific viruses.

Placing and replenishing your defences is key. What may look solid is actually fairly penetrable in practice, with some viruses slipping past critical defences unscathed. The viruses themselves are also flexible enough to keep the contests tight – some releasing further viruses when you manage to take them down, complicating issues to a greater degree.

It's perhaps obvious therefore that this is no easy game, and one that for many will be over in a matter of minutes – the grid shutting down when too many of the viruses make it through. But this isn't a bad thing, as the quick, accessible nature of FIREWALL means it's no ordeal to have another crack. Of course, you have to go through that old classic trial-and-error rigmarole.

What is more of an issue is the tendency for FIREWALL to crash from its title screen, causing the whole iPhone to freeze up without warning. This happened a good 50 per cent of the time during this review, making each restart stifled by trepidation.

If this could be addressed in an update, then Solus could be on to a winner here – FIREWALL is most certainly not the most complicated of titles, but it's challenging and especially well presented. You may never get past the first few minutes, but then that's not really the point. It's the trying and learning that makes this a sound iPhone investment.