General Discussion Need I be worried about malware?

No need to worry. iOS systems are one of the safest. Every App in iOS has been reviewed by Apple.

 

As I understand it, you're safe...

Each QR code has a tag that identifies its purpose (common ones include: contact, url, text, encrypted text, etc). Even in the early days, in Japan, they were used for payment at vending machines for food and tickets. But the tags that are used are at the discretion of the app designer, and could be entirely exclusive to the app (as mekorama's QR code is bound to be).

What happens when you scan the code? The app you're using to scan the code (in this case the mekorama app) checks for the tag that it is designed to process. If it can't find such a tag, then it will reject the code. Otherwise it will interpret the rest of the message in the code according to an algorithm that is looking for a specific pattern of data that defines a mekorama 3d level. If this part of the message is corrupted by a hacker, then you will simply get a garbage level, or the entire image will be rejected as un-scannable, depending on how the app's author has designed his app.