"Copy of a" is the second single from the Nine Inch Nails album Hesitation Marks. The single was given away for free on Amazon.com for a limited time starting August 13, 2013 to anyone with a US or UK account. It was also made available to those who had pre-ordered the album from Nine Inch Nails' official online store, together with "Came Back Haunted" in a zip file labeled "Hesitation Marks Singles". The song was played live in concert for the first time about two weeks before the official studio track was released.
When referring to the song, Marc Hogan of Spin magazine had stated "The concept of "a copy of a copy" is somewhat quaint in a time when digital files can be copied limitlessly without any discernible drop in quality." Hogan had also described the drum machine in the song as "crisp" and the synths as "jittery", while noting the "overlapping vocals and smeared tendrils of fuzzy noise". Andrew Trendell of Gigwise described the song as "an epic, sprawling and typically NIN number that features a gradual and repetitive trancey build-up with a dark intensity before an almighty rock crescendo." He also interpreted the song's lyrical theme as "a struggle for identity."Triple M Network inferred from the song that "Trent Reznor stays true to his roots while trying something different." Similarly, Forrest Wickman of Slate magazine stated that "the song is an update on an old NIN sound", while speculating on the possible muse on the postmodern condition or Fight Club on the lyrics. He also praised the musical beats by Atticus Ross and Alan Moulder and the use of Swarmatron.This Is Fake DIY also referred the song "as a punchy electronic piece, suitably harsh on the senses."Fact magazine described the song as "an urgently paced but slow-building chiller constructed from ice-cold techno arpeggiations and droning synths", while Katie Hasty of Hitfix remarked the mellow vocals. She also praised the effect of looping sampler and itchy beat, contrasting it with the features of the previous single, "Came Back Haunted."