Flobo WipeTheDisk is the best utility you need to securely erase all traces of your activity on computer. Don't leave your secrets on your old HDD. Deleting a file, partitioning a disk, or formatting a hard drive will not erase your data!
Just run FloboWipeTheDisk and select area of your hard disk: whole partition, whole hard disk wiping process. It erases all viruses including master boot sector viruses (if erasing hard disk is specified).
See also: Wipe data on your disk