No clue, they've never said.
If I were to hazard a guess I'd say it was FastBloc , cause they are cheap and easy to use...
Here's some background on it http://www.wikinvest.com/stock/Guidance_Software_(GUID)/Fastbloc_Write-blocking_Hardware_Software
FastBloc® hardware and software is used to connect EnCase® Forensic to a hard drive to which investigators have physical access. FastBloc® hardware acts as a middleman between the operating system and the hard drive and physically blocks any hard drive write requests. This is a system primarily used by law enforcement and is designed to provide the investigator an extra level of protection against the possibility of original evidence being damaged on the hard drive.
FastBloc® SE is the first commercially available software write-blocking solution that allows EnCase® Forensic to take full control of IDE, SATA and SCSI channels on particular PCI controller cards, as well as the FireWire and USB ports from Windows, thereby permitting an extra level of protection against damaging original evidence without the use of hardware write-blocking devices. In addition, FastBloc® SE allows forensic investigators or consultants to override and access host-protected areas and device configuration overlays.
What do you think?