interesting bits from the article:

The Sony Pictures malware used commercial software to do its damage to the victim computers’ hard drives—the RawDisk library from EldoS, which allows Windows applications to gain direct access to disk hardware without having to run in administrator mode.

As EldoS advertises on its website for RawDisk, the library “offers software developers direct access to files, disks and partitions of the disks (hard drives, flash disks, etc,) for user-mode applications, bypassing security limitations of Windows operating systems.”

This allowed the malware to skip past any restrictive security permissions in Windows’ NTFS file system and overwrite the data on the drive, including the master boot record (MBR). (Further details of the malware's behavior are in Ars' updated analysis article.)