Yes you can carry a hard disk to the US with movies downloaded from a torrent

[Wilhelm]

Just keep it like in a backpack in a hard drive case and maybe change the name on the files. 

Many times it is not the inbound US customs that will be the check point but outbound from the country you are leaving. The RIAA, has been very aggressive in pushing anti-piracy policy within international trade agreements and countries like Vietnam have negotiated back saying they will not police copy right infringements within the boarders of the country, but will search for outgoing material… Since privacy & property rights are dictated 1st by the local laws and 2nd by international law once you clear customs, the expatriate country has carte blanche in dealing with your belongings.

For example, Vietnamese customs confiscated DVD’s I was bringing home to my parents a few years ago, and more recently some hard disks I had packed in my baggage were degausse erased with out my consent or knowledge.. imagine getting home and finding all of your Tax records and family pictures are gone.

If you want to be sure to keep your files 

1) Bring only 1 HDD (more than one brings suspicion of trafficking material)
 - or bring the HDD’s as an complete computer.
2) Put the files that might upset the RIAA in a hidden encrypted partition
3) Carry any HDDs or the external drives as carry on .. at least you will know what is going on and it is more difficult for them to devote a lot of attention to you as there are long lines of people to be served.