05/12 completely Delete data in Harddisk

Suppose sometime u need to delete the entire data in ur HDD so how to do that securely so that whenever someone try to recover data he/she gets nothing but rage. ;-)
there are many tools available for it many softwares are there know as shredders etc. but u dont need to buy them this way is free and cost nothing. Do as below

Format ur harddisk but thats not enough during format surely change the File system that is if it was NTFS change it to FAT and vice-versa.