If you're upgrading to a new computer, be sure to properly delete any highly sensitive information, such as credit card numbers, tax returns, driver's licenses, social security numbers, and your business' customer's confidential information. Note that simply deleting the files does nothing for security -- and in fact -- even reformatting your disc drive is not sufficient.
Keep in mind that information thieves have very powerful software that can retrieve data that most of us thought was long gone. So, depending on what type of information you had on your computer, here's what you should do to clear data from your hard drive before selling, donating or recycling it.
1. Gather all your personal files and put them in one folder.
2. Encrypt the entire folder using encryption software. If you don't have the software, there are dozens of free ones available you can download, such as TrueCrypt.
3. After successfully encrypting the folder, use a "wipe" or "shredder" program to completely clear the hard drive. Once again, if you don't have the software, download one, such as Wipe File or DP Shredder, for free.
4. Reformat the drive and reinstall the operating system.
5. To be certain your drive has been completely erased, run a data retrieval tool like Disk Investigator to examine the raw data on the disk. You can search for keyword, like "social" or "certificate" to see if anything comes up.
If you follow the steps above, even the CIA will have trouble retrieving your data. But, if it's vitally important that nobody ever see the data again, you should totally destroy the hard drive, especially the CD-looking platter inside the drive.