An empty USB port at a charging station in an airport, a mall, or some other public place might seem heaven-sent to someone with a rapidly dwindling phone battery and a USB cable that’s missing its outlet cube. The FBI’s Denver base recently tweeted a recommendation that people “avoid using free charging stations” because hackers “have figured out ways to use public USB ports to introduce malware and monitoring software onto devices.” Make sure your USB cable has its wall adapter so you can plug your charger right into a power outlet, or bring a portable charger with you whenever you anticipate needing to charge your phone in public.