Hidden TrueCrypt volumes
"That's why things like TrueCrypt with hidden volumes were invented."
The point is you shouldn't need to hide it. Why should they be able to just look through whoever's personal files they feel like, without any reason. Of course it is keeping us safe from terrorphiles so it's ok.
Also what do they hope to achieve by doing so, and having a cursory browse of someone files. That the person will be travelling with an entry in their contacts for 'Terrorist Bob- Sleeper Cell Leader'. Or a file on their desktop called 'Secret Hijacking Plans'. Border security is ridiculous - airport security in particular.