Schneier on Security: QR Code Scams
www.schneier.com/blog/archives/2012/12/qr_code_scams.html
What Jamie wrote
I don't know that I will ever scan a QR code, but I surely would never scan one using a tool that doesn't ask for my approval before going to the target URL. It should also ask for my approval on every redirect that is sent as well.
One of the warning signs seems to be a sticker with the code, rather than a code embedded in an advertising poster.