After detailed forensic analysis … it was determined that the CPU corrupted the angle of attack (AOA) data, erroneously relabelling the altitude data word so that the binary data that represented 37,012 (the altitude at the time of the incident) would represent an angle of attack of 50.625 degrees.
The root cause remains unknown. “Experts are still not sure of the root cause of the malfunction in the data unit, but subsequent software changes by Airbus mean any similar error in the future won’t lead to another terrifying nosedive.”
via this tangentially related discussion on HN (“A Boeing Code Leak Exposes Security Flaws Deep in a 787’s Guts”)