Get the Whitepaper called Using QR Tags to Attack Smart Phones (Attaging). It discusses the threatscape related to arbitrary scanning of these tags and using Metasploit to exploit them.
You can download it from the following link: https://packetstormsecurity.com/files/download/105029/attaging.pdf
Source: https://packetstormsecurity.com/files/105029/Using-QR-Tags-To-Attack-Smart-Phones.html