Wiping your hard drive? One pass will do it

One of the most tenacious myths in the tech world has involved how to delete the data off your hard drive. First off, it's common knowledge that putting a file in the Recycle Bin and emptying the trash does nothing to actually delete the file, you have to overwrite the space where the file once was with something else. But with what?

Paranoid techies will tell you a drive or file has to be overwritten numerous times with random data in order to "securely" delete it. Some say seven times. I've even heard 13 and a whopping 35 times -- just to be sure, they say. (The real nuts don't mess with software and instead tell you to drill holes in the drive to kill it for good... which is awfully wasteful if you ask me.)

But is all that rewriting (which can take days to complete) really necessary? A few years ago I sent a hard drive that had been overwritten with a single pass of zeroes to a high-end professional data recovery firm and they declared all the data on the drive completely unsalvageable, and that's the advice I've given to users ever since: A single overwrite will ensure your personal files are gone for good.

And now I have independent, scientific confirmation: Forensic scientist Craig Wright overwrote drives once under controlled conditions and examined the drive surface with a magnetic-force microscope to see if any traces of data were recoverable. In a nutshell: Nope. If you know exactly on a drive where a byte once existed, the probability of recovering that byte in full is less than 1 percent. And of course, that byte corresponds to a single character of a single file. The odds of recovering even, say, a 10-character string would be infinitesimally small (less than 7.4*10^-21 percent, if you must know)... and even then you'd have to know in advance exactly where to look for the characters in question.

As the linked story notes: Rather than waste time worrying about deleting a file 30 times, you are better off making sure you delete and overwrite all the copies of a file on the hard drive. In Windows, that means regularly deleting temporary files and overwriting free space with zeroes. Of course, if you're wiping an entire hard drive from start to finish, you needn't worry about deleting individual files at all: One overwrite with zeroes will take care of everything.