When you plug in an external storage device, a USB stickor an external hard disk, Tails 6.0 mounts it automatically. If the storage device contains an encrypted partition, Tails 6.0 offers you to unlock the encryption automatically.
If an attacker manages to plug a [[!wikipedia BadUSB desc="malicious USB device"]] in your computer, they could run software that breaks the security built in Tails without your knowledge.
[[!img test_6.0-rc1/usbguard.png link="no" class="screenshot" alt="Notification: Reconnect USB device. New device has been detected while you were away. Please disconnect and reconnect the device to start using it."]]