Have you seen the free USB charging stations in airports, hotels and other locations? These are for you to attach your phone to and to charge the battery on your phone for free.
These are usually good things to use, however they can be abused and do harm to you.
The USB connection can be used to charge the battery on your phone and it can also be used to transfer data to your phone or from your phone. Many people use the USB connection to download pictures from their phone to their computer.
People can set up USB charging stations to do more than charge your phone. They can use the charging station to upload malware (viruses, trojans, programs to send your information elsewhere, etc. They can also use the charging station to steal data from your phone including passwords, account numbers, etc. When the charging station does these extra things, it is called juice jacking.
There are several ways to protect yourself from these. The first is take an extra phone battery with you and donít need to charge your phone. Second is to carry your charging unit with you so you can just plug in an electrical socket and that is safe. Third thing you could do is buy and use a USB cable just made for charging. This cable would not have the pins connected that carry data. The limitation will be that you will need to know which cable it is to use then (the plugs are the same) so as not to confuse with your data cable, if you did you would see it would refuse to download your pictures.
Most charging stations are safe, but you have no way to know looking at them and it would not be as easy was seeing if someone stuck a skimming device on a credit card reader.
Turning off the phone while charging would help but the scammers can get around that and read data off your phone when plugged in their stations if they do some extra work.