The official soundtrack included in the Assassin's Creed: Brotherhood Digital Deluxe version is reported to be sourced from pirated files.
A Reddit user reported that the MP3 files included with a purchase of the Digital Deluxe Edition have the note "encoded by arsa13".
This same credit apparently appears on illegal torrents of the Assassin's Creed: Brotherhood soundtrack released by pirates in FLAC form, ripped from the game's own files.
To join the dots, this suggests that when it came time to bundle the soundtrack for inclusion in the PC edition, an Ubisoft staffer may have converted the pirated files rather than find an official source.
Thanks, Voodoo Extreme.