When you delete a file, the operating system does not destroy the file contents from the disk - it only deletes some "references" on the file from some system tables. The file contents remains on disk until another file happens to overwrite it. Any software recovery tool can restore the data if it hasn't been overwritten or thoroughly erased. Hardware recovery tools may even restore overwritten files by analyzing latent magnetic traces.
As a result, your confidential information may be lying unprotected on your disk (not wiped, overwritten or erased) and it is almost impossible to prevent it from falling into the wrong hands.
east-tec Eraser offers secure wipe methods that meet and exceed not only the U.S. Department of Defense standards, but also several other international secure erasing standards, such as Peter Gutmann, Bruce Schneier, AFSSI, NAVSO, Russian GOST, German VSITR. By using these methods, you make sure your data is erased for good.