Many people worry about credit card numbers being stolen when used online. Indeed, that is a good thing to be concerned about but online theft of credit card numbers is extremely rare. Others worry about someone stealing identity theft information from genealogy sites. That, too, is a valid concern but is unusual. In fact, such methods are difficult and would-be thieves can find much easier methods to steal your personal information.
Writing in the MakeUseOf web site, Kannon Yamada describes one very easy method to steal all sorts of personal information: obtaining a used PC that had not been purged of the previous owner's information.
I will suggest that all computer owners need to read Kannon Yamada's article at http://www.makeuseof.com/tag/how-to-get-your-identity-stolen-in-one-easy-step/.
Before you sell, give away, or throw away an old computer, you need to completely erase the hard drive(s). Just using the Windows delete commands won't do the job as there are a dozen or so utility programs that will undelete previously-deleted files. Instead, you need to wipe the hard drives clean, leaving nothing behind. You can find three different ways of doing that at http://www.wikihow.com/Erase-a-Computer-Hard-Drive.
I like a fourth method: remove the hard drive(s) from the computer, find a very heavy sledge hammer, and then pound the drives vigorously. Several times.