The final component of securing your data is making sure that any files you want dead are really most sincerely dead, and for this task you must turn to disk- and file-removal tools. Using the standard Windows Recycle Bin merely removes the visible reference to the file and marks the space as available; Windows does not truly delete any data until something overwrites that data, and may leave large chunks of recoverable data visible. Those leftover chunks allow undelete and to work; the trade-off when you use strong file-removal tools is that you won't be able to restore accidentally zapped data easily, unless you've previously backed it up on another source.
"Secure" deletion is the subject of much discussion. A 1996 paper by of the University of Auckland produced a value of 35 passes, but these days that number is generally considered far too high due to increases in drive density. The "35 passes" number has become, in the words of the author of the original study, "a voodoo incantation"--but it's often a standard in many workplaces nonetheless. The programs discussed here all support a variety of data-erasure algorithms, including the 35-pass "Gutmann" standard.
The free and open-source utility allows you to select files or folders to be deleted, or it can wipe free space with several different algorithms. Although I experienced no issues with it, development on it has ceased, which makes it a risky choice as file formats evolve; new disk formats, security changes, and file systems appear fairly regularly, so a lack of active support can mean security problems. Also free (but not open-source) is , a suite of system-scrubbing utilities that sweeps up temp files, cookies, recently opened file lists, Registry clutter, and more. It offers the ability to scrub free space or to wipe complete volumes, as well as the freedom to choose specific files or folders (and specific file types, such as all *.xls files in a given folder) or to exclude specific files from general rules.
The commercial package ($50, 15-day free trial) has a wide range of functions arranged around the task of scrubbing unwanted data, from deleted files to Explorer search terms. It produces detailed reports, turning up quite a number of tiny file fragments cluttering up space, some of which contain readable data. It also adds a right-click menu option to erase a file securely, always a nice touch. However, I encountered a fairly serious flaw: When the scanner reached a file with non-English characters in the name, it would simply hang. This problem can manifest in surprising ways; I discovered it because SecureClean balked at the foreign-language templates in a desktop publishing program I use. This is a known bug in SecureClean 4 running on Windows 7 64-bit machines, and the vendor plans to fix it in the upcoming version 5.
Finally, sometimes you just want everything gone, such as when you're recycling or donating an old system. CCleaner has a drive-wipe function, but you might also check out the descriptively named , aka DBAN. This is a straightforward program, as it comes as an ISO disc-image file. You burn the image, and then boot a computer with that disc; the utility then seeks out and destroys all data on the computer's hard drives.