File Monster completely erases files from your system, actually overwriting the information in the file so it can not be recovered. The reason information is still available when you delete files with normal deletion methods is because normal deletion methods only tell the operating system to not recognize the file as being present anymore, yet the information hasn't really been erased. As a result, anyone with a little knowledge of computers can very easily recover the information you thought was erased.
To take your privacy a step further, File Monster also overwrites the original file name with a random name and it changes the file's creation date. Moreover, it can even erase pesky hidden files, system files, and read-only files.