A bit back, I looked over Stavrou's USB smartphone paper.  Interesting research.  Well done.   All one needs to do is take a tacticle jacket, malicious usb-enabled laptop, spraypaint a large, trustworthy brand name, then head to your local concert venue.  If one is paranoid about victims stealing the USB cords, epoxy the cords to your ports.  While walking around the venue, look for those on their phone.  Once discovered, ask them if they would like a free charge.   Before you know it, you will look like the following;

Easy as apple pie.

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