Let's remove files in your hdd once and for all!

Most people are not aware the delete button on your operating system does not in fact delete the file content itself but it removes the pointer to that content within the hard drive space. Therefore, unless it is overwritten by some other file or some other contents, it will stay there for a long time. This is basically what data recovery service provides. They try to recover the un-overwritten content in your hard drive to recover what once was "deleted." This can pose problem if you have sensitive data within the computer that you are using. If you need to throw away your old computer, you better clean out your hdd content, otherwise, someone else can get hold of your personal data!

Robin Harris have excellent article on How to REALLY erase a hard drive