I think this is just an another example of online system being hacked, and not specific to QR Code system. 7 Pay system was hacked in less than 4 days of start of the service, this suggest that it is unlikely that hackers figured vulnerability of the system within few days but possible that insiders were involved and hackers were working on hacking the system way before 7 Pay went into the service to public.

When security audit is done on computer systems, always comes out that weakest point is human factor. People working on the system, as it be system engineer or customer service, knowingly or unknowingly gave out information to hackers looking to hack the system.

It is a very bad publicity for 7 & I Holdings which operates 7 Pay system and 7 Eleven convenience stores. True, it is possible that 7 Eleven is now in further disadvantage in market of cashless payment system.