You are on a U.S. military aircraft, transporting hard drives with important, classified information, when you collide with another plane and are forced to land near an enemy intelligence agency. There is no time to delete the files, and the drives are in heavy-duty steel cases so that they are difficult to destroy. You have a few minutes before someone finds you, grabs the drives, and searches them for even the smallest trace of useful data. What would you do?

Michael Knotts, a senior research scientist at the Georgia Tech Research Institute, dealt with this question after a U.S. plane collided with a Chinese fighter jet and was forced to land near what he called “China’s premier signals intelligence department” four years ago. At the request of defense contractor L3 Communications, he and other researchers developed a method for quickly erasing hard drives by cranking them through a mechanism with a powerful magnet inside.

Click to see: A prototype of the "Guard Dog"

Knotts explains that the device, dubbed the “Guard Dog” by the researchers, requires no electricity and is powerful enough to overcome the magnetic shielding effect of steel casings.

“The [National Security Agency] has to destroy about 30,000 hard drives a year,” Knotts says. “Presently they do it by grinding them into powder or magnetically degaussing them” with a large electromagnet. These methods don’t work when there’s little time, power, and space.

Click to see: Image of an erased hard drive

He adds that although software-based “shredders” such Norton WipeInfo can delete and overwrite files several times to ensure that they cannot be read again, they are not powerful or fast enough for some military applications. These programs can take hours to erase a drive, he says, and they might leave some data behind. “A lot of approaches to erasing disks do only a partial job,” Knotts says.

He explains that when a portion of a hard drive is found to be unstable, the drive automatically disables access to that region. All programs, including “shredder” software, are unable to write or read from these “sequestered sectors” and so cannot remove data that might be left in them. Theoretically, he says, a determined investigator with knowledge of how the drive works could find these sectors and read them, revealing a few important pieces of data.