Deleting a file in Windows doesn’t mean that it disappears forever. The system simply marks the space as free again, but the actual file is still there and can easily be recovered with the appropriate software.
So if you want to make sure your deleted files can’t be recovered later on, use Freeraser, an alternative Recycle Bin for Windows that erases files securely so that they can’t be retrieved with a recovery tool. The program features a nicely-designed resizable icon with transparency effects, which looks much better than the standard Windows bin.Freeraser supports three deletion methods (fast, forced and ultimate) and works really efficiently. Just bear in mind that you need to be sure you want to delete those files: although the program lets you stop the deleting process, it doesn’t have an “undo” option. Also, it would be great to have it included in Windows context menu, just like the Windows Recycle bin is.