Chances are you’ve been at an airport, on a bus, or some other public space and your smartphone’s battery was about to die. More and more of these spaces offer convenient and free USB charging jacks. Before you reach for your charging cord, you should understand that there are security risks with these free power ports and learn how to protect yourself.

The possibility for hackers accessing your phone and data via USB charging ports has been proven repeatedly at hacker conventions and by security researchers. Security expert Brian Krebs was the first to report on this attack and coined the term “juice jacking” on his blog, Krebs on Security. To date there haven’t been any real-life attacks reported, but the way sneaky people sneak, it may just be a matter of time before this vulnerability is exploited. You can start protecting yourself now to avoid problems in the future.

There are several ways to avoid the risk. The most sure-fire way is to avoid using the charging ports at all. If there are outlets available, use the AC adapter that came with your device.

If there are no outlets available, you can use a portable USB battery.

But if you want to be prepared in the event neither of these are available to you, you could use a USB data blocker.

USB data blockers, also known as USB condoms, keep your device and data safe by cutting off the pins that are used to transmit data through the USB cable and allowing only the power pins to connect on through. They are small devices that plug directly into the charging port, and the charging cable gets plugged directly into the blocker.

The original no-frills USB Condom can be purchased for $7, while the new updated version called SyncStop is $12.99. There are other data blockers on the market but SyncStop has been around for a while and been recommended by security experts.

Some security companies have already implemented policies for employee safe charging rules. You may want to consider adding this to your employee handbook with your other security policies. You can also make it easy for them to follow the policy by providing the right tools- a spare AC charger, a portable USB battery, or a USB data blocker for each staffer’s devices.