And then you are fucked because you can't update the firmware to the trusted, signed open source version.
Re:Yubico: Secure Hardware vs. Open Source
by discreditable on Tuesday May 17, 2016 @01:03AM
(#11711452)
How do they do that to begin with?
There's been various news on this, like (first Google search I came across): http://www.geek.com/news/nsas-top-hacking-unit-intercepts-ma...
This does not close the attack vector of someone intercepting the device before you get it and surreptitiously installing firmware with a backdoor.