I'm not sure how to hammer this point home, so I'll put it as forcefully as I can: Protect your data!
We’ve covered how to keep data private on your current computer, but what about one that will no longer be in your possession?
Federal officials suggest using a hammer:
The hard drive should then be subjected, in a suitable facility with individuals wearing appropriate safety equipment, to physical force … (e.g., pounding with a hammer … ) that will disfigure, bend, mangle, or otherwise mutilate the hard drive so that it cannot be reinserted into a functioning computer. Sufficient force should be used directly on top of the hard drive unit to cause shock/damage to the disk surfaces.
The San Jose Mercury News discovered that gem of advice from the National Institute of Standards and Technology. “Other methods commonly used to eliminate stored bank records, Social Security numbers, and other confidential data can’t always be counted on to work,” the site says. It points to the story of two MIT graduate students who bought used hard drives on eBay and found everything from credit card numbers to old emails and medical records.
Trusting a recycling service to do the job for you also isn’t ideal. Some just collect spare parts and pass on the rest to other companies, the Mercury News says. You never have proof your data was wiped and the device destroyed.
If you want to sell your used devices instead of pulverizing them into worthless scrap, wipe their memory as best you can, while realizing you may not get everything. For PCs, DP Wiper is a free option that overwrites files with random data. Some experts suggest overwriting at least three times to be thorough. For smartphones, Lifehacker has a guide for both Apple and Android devices.