Composer Harry Gregson-Williams wrote that most of the music featured in Blackhat (2015) is not his, even though he's given on-screen credit. He expressed his disappointment on Facebook right after the premiere, when he had discovered for the first time that director Michael Mann only used a small part of his original score. His since-deleted post said: "I would like it to be known for what it's worth that the 'score' for Blackhat maybe credited to me, but contains almost none of my compositions. I attended the premiere of the movie at the end of last week and discovered, to my horror, music that shocked and surprised me... quasi emotional (synth) string pieces that I'd never heard in my life before. I knew of at least one other composer, a good one at that(!), that had put in months of work on this movie just as I had, but this appeared to me to be in addition to both our contributions. I can say nothing for certain except that I was not the author of most of what is now in the movie." Most of Gregson-Williams' work was replaced with compositions by Atticus Ross and Leopold Ross. Additionally, five themes originally composed by Ryan Amon for the score of Elysium (2013) were re-used in Blackhat (2015).
The film's plot was inspired by the Stuxnet's case, a computer worm designed to attack industrial programmable logic controllers. Discovered in 2010, Stuxnet ruined almost one-fifth of Iran's nuclear facilities and its origin couldn't be officially identified.
The title "Blackhat" refers to the term that describes a villain (named after the practice of villains in Westerns wearing black hats). In hacking, a black hat hacker will commit cyber-crimes for maliciousness or for personal gain.
The writing credits in early promotional material read: "Story by Michael Mann and Morgan Davis Foehl. Screenplay by Foehl and Mann", but Foehl received sole "Written by" credit following an arbitration conducted by the Writers Guild of America.
A diverse set of digital cameras, including small consumer cameras, were used during production to create rich and diverse textures. The subtle changes in resolution and look can only be fully appreciated if you see Blackhat (2015) in the 4K master resolution on a big screen.
After the disappointing US box office results Universal Pictures International opted not to release the film theatrically in Australia on 25 February 2015 as originally scheduled and released it straight to DVD/BluRay instead. In Belgium and other markets it went straight to DVD/BluRay, too.
Michael Mann had final cut on the theatrical version, but he continued to work on the film after the release. In February 2016, Mann presented an alternative Director's Cut at the Brooklyn Academy of Music, which hosted screenings of his work. According to reports the new version added some material, deleted other material, had some important sequences in a different order and used some alternative footage, but the film still told the same story. Since Mann reportedly took notes while watching the new version with the audience, this was probably not his final version. It is not known if and when a new cut will be released.
During one of the code analysis scenes, on the right side of the computer screen there is what first appears to be gibberish words. The words, however, are merely backwards and reads as "what to do or what not to do, but she's afraid either to cross her legs or press them together. She sits with gloved hands braced on either side of her seat." This is actually an excerpt from the book Story of O aka Histoire D, written in 1954 by French author Anne Desclos under the pen name Pauline Réage. The novel, which has themes of BDSM, was inspired by the work of the Marquis De Sade.