Simply deleting a file doesn’t necessarily mean it’s deleted. Even formatting a drive doesn’t actually destroy all those bits and bytes. In both cases, the file system simply deletes the internal “shortcuts” to such files and leaves the actual data on disk -  at least until it gets overwritten by new data. Which means anyone with basic recovery tools and access to your PC is able to restore such files. 

That’s why TuneUp Utilities 2012 contains a data wiping tool called “TuneUp Shredder”. It  destroys data by using standardised procedures and several methods of deletion which guarantee the data can never be recovered:

• Fast delete: Data is completely overwritten with single characters.
• Secure delete in accordance with U.S. government guideline: Files are overwritten multiple times with specific data patterns before deletion (standard procedure of the U.S. Department of Defence)
• Secure delete in accordance with the Gutmann method: The data to be deleted is overwritten in 35 stages, with random values in accordance to a special pattern, before being deleted (per Peter Gutmann).