“The Wi-Fi Pineapple is a tool that makes fake Wi-Fi hotspots that automatically match the name of whatever network devices have previously connected to,” says Ben Miller, a Wi-Fi consultant and blogger with Sniff Wi-Fi.

Miller says the Wi-Fi Pineapple connects to laptops, smartphones, and tablets two different ways. One way is by programming the device to send out a commonly used SSID (that’s the “service set identifier,” also known as a Wi-Fi network’s name) that’s identical to ones that are popularly used. So that “Marriot_Guest,” “hhonors” or “gogoinflight” network that your computer or mobile device detects may be a trap.

The other way Wi-Fi Pineapple locks onto devices is even more insidious, using your “trusted networks” against you. Computers and mobile devices all have trusted networks — they’re the legitimate Wi-Fi networks that your gear connects with every day, including your home network, your work wireless connection, and the one at your favorite Starbucks, for example.

Android and iOS devices are somewhat safer because they probe in different ways. But you should still be sure to shut off your Wi-Fi if you’re away from home or the office.