When you plug your smart phone into a USB cable, your device will try to pair with the device on the other end of the cable. If the only thing on the other end of the line is your personally owned USB charger, no worries. But if you plug into a public charging station or a stranger’s USB charger, you are opening yourself up to malware. The device on the other end can pair with your phone and cause all sorts of mischief.
The soon-to-be-released USB condom is a dongle that sits on the end of your USB cable and prevents data transfer, meaning you can safely charge your device without fear of contracting malware.
I like the idea of the device, though I think a better answer is a USB cable with a switch built in, to toggle between data and charge-only modes.