The Federal Bureau of Investigation is warning people against using free phone charging stations at places like airports and shopping centers.

In a tweet from its Denver office, the FBI said “bad actors” can use the devices to steal your data.

“Avoid using free charging stations in airports, hotels or shopping centers. Bad actors have figured out ways to use public USB ports to introduce malware and monitoring software onto devices. Carry your own charger and USB cord and use an electrical outlet instead,” the agency said.

On its website, the FBI describes the process as “juice jacking.”

“USB power charging stations in airports, hotels, and other locations because they may contain dangerous malware. USB connections were designed to work as both data and power transfer mediums, with no strict barrier between the two,” the FBI said. “As smartphones became more popular in the past decade, bad actors figured out they could abuse USB connections to hide and deliver secret data payloads that a user might think was only transferring electrical power. This is called “juice jacking.”

Here are some tips to protect your information:

• Avoid using a USB charging station. Use an AC power outlet instead.
• Bring AC chargers, car chargers, and your own USB cables with you when travelling.
• Carry a portable charger or external battery, and only use your own, personal cables purchased from a trusted supplier.
• Consider carrying a charging-only cable, which prevents data from sending or receiving while charging.