Recently a physical attack vector on the Trezor One hardware wallet was disclosed by a security researched called Sunny, Trezor was quick to release a firmware update 1.6.1 but the researcher realized that another attack vector of the same type was possible so SatoshiLabs released the new firmware update 1.6.3 on the 30th of August.
Trezor comes with a tamper-evident seal and the attack vector only affects tampered devices, so if you bought your Trezor used or if it came with the seal broken, make sure you update the firmware first then set it up. If you’re updating an older Trezor, make sure to have the correct recovery seed on hand as you’ll need it to set it up.
The newest firmware verifies the authenticity of the bootloader in the device. The bootloader checks the signature of the firmware. If both are genuine, your device will not display a warning, and therefore your Trezor is safe to use.