QR code found on residential bulk mailings

There is sometimes mystery and drama about who sends out bulk rate mass mailings that feature a commonly seen form of machine-readable-only bar or "QR" symbol code. A legit mailing, coming from a trusted source, might launch browsers to an Internet site that is safe, only there to provide "more info" but QR codes work automatically, browse to an unknown URL faster than any human could react. Often there is failure to mention what to expect or show in plain language what the QR payload is going to do. QR codes can be scanned for safety with paid security apps but most mobile devices lack that by default.  The risk is similar to clicking "unknown" URL links. There is wide acceptance for square-shape QR codes convenience so no suprise they are often a way to exploit their benign appearance to harvest information -- from the unwitting curious seeking to get info, not give info instead.