IRATEMONK: NSA Exploit of the Day

Today's item from the NSA's Tailored Access Operations (TAO) group implant catalog:

IRATEMONK (TS//SI//REL) IRATEMONK provides software application persistence on desktop and laptop computers by implanting in the hard drive firmware to gain execution through Master Boot Record (MBR) substitution.
(TS//SI//REL) This technique supports systems without RAID hardware that boot from a variety of Western Digital, Seagate, Maxtor, and Samsung hard drives. The supported file systems are: FAT, NTFS, EXT3 and UFS.
(TS//SI//REL) Through remote access or interdiction, UNITEDRAKE, or STRAITBAZZARE are used with SLICKERVICAR to upload the hard drive firmware onto the target machine to implant IRATEMONK and its payload (the implant installer).l Once implanted, IRATEMONK's frequency of execution (dropping the payload) is configurable and will occur when the target machine powers on.
Status: Released / Deployed. Ready for Immediate Delivery
Unit Cost: $0

Page, with graphics, is here. General information about TAO and the catalog is here.
In the comments, feel free to discuss how the exploit works, how we might detect it, how it has probably been improved since the catalog entry in 2008, and so on.