Along with your money, the QR code also steals your personal information, (depending on the app and y settings) social networking usernames, phone number, whatever.
I recommend using a QR scanner that shows you the page that the code points to, before it goes there. ZXing is one of those that give you the “preview” – there are others, but many do not show you and give you a chance to cancel before linking to a site.
In a report by the International Business Times, Chinese digital marketing firm China Channel claims that many beggars they encountered in Beijing “are actually being paid by local businesses and startups to promote QR codes and entice passersby to scan them.”
The scans are then used to harvest user details from their WeChat IDs, which are then sold to small businesses for unsolicited advertisements.