When cleaning a system for transfer, don’t use the Recycle Bin to delete files. Even when emptied, “deleted” files are still easily recovered, since the built-in delete mechanism simply makes the area on the hard drive where the old file was stored available to new files. Instead, use a “file shredder” program, which overwrites the file multiple times before erasing it. Almost a dozen free shredder programs are available from Snapfiles.com
You should delete other personal data, too. From your e-mail program, delete any inbox or stored messages, and compact all folders if there is such an option. Delete any contacts in the address book, and remove any server/log-on account information. From your Web browser, delete your bookmarks and saved passwords, and use a program like CCleaner to delete things like your browser’s history, cache, cookies, temporary files, and so forth. If you use AOL or a dial-up or PPPoE Internet connection, delete any accounts or connection passwords.