Here’s an expanded comment I posted to Computerworld recently. Re-using an old hard drive yourself, by putting it in an external drive enclosure and using it for backup is fine. (I have one in a safe deposit box, in case my house burns down). But don’t donate it, sell it, or even recycle it unless you destroy the data on it properly first.  RB

Recycle an Old Laptop Hard Drive

RB comment: Just be sure to destroy the drive if you are finished with it. Unfortunately, donating it /selling it are not wise. You can also do a “secure erase,” which encrypts the old data and allows the drive to be safely reused. Reformatting the drive, and running the various utilities that supposedly overwrite old data, are NOT substitutes, because they don’t get at the underlying data thoroughly. And tests of drives purchased on eBay still show about half of them have proprietary data, including financial records etc.

Here is one such academic study: Remembrance of Data Passed: A Study of Disk Sanitization Practices. There are many others.   Here’s a good popular article.

Here is an explanation of safe erasure. http://cmrr.ucsd.edu/people/Hughes/DataSanitizationTutorial.pdf

For physical destruction, the easiest method is a hammer applied to the spindle. Once the bearing has “wobble” in it, the drive can’t read the tracks any more, and it would take an NSA-level lab to recover data, even partially. You can also smash the circuit card. It can be replaced, but the thief has to work much harder to find a compatible card.

By CHRISTOPHER DREW  Published: January 10, 2010

HAMPTON, Va. — As the military rushes to place more spy drones over Afghanistan, the remote-controlled planes are producing so much video intelligence that analysts are finding it more and more difficult to keep up.

Air Force drones collected nearly three times as much video over Afghanistan and Iraq last year as in 2007 — about 24 years’ worth if watched continuously. That volume is expected to multiply in the coming years as drones are added to the fleet and as some start using multiple cameras to shoot in many directions.

via Military Deluged in Drone Intelligence – NYTimes.com.

[Actually I'm surprised that the 24 multiplier is not higher, especially since some drones operate at night. On average, only 24 cameras are running.]