Or if you use a USB storage device such as an external hard drive or a pen drive, then having the ability to easily wipe out data without giving any chances of recovery becomes crucial. There are many software utilities available for that nowadays but some only run in the OS itself thus if you want to wipe a HDD, USB, etc that doesn't have an OS then you'd have to go through a bit of a hassle (unless you wanna manually attach that drive to your computer).
In that case, if you're looking for a free software application (has a separate professional version but the free one is more than enough for most of our needs) that runs inside MS Windows + also lets you boot into a boot-able environment of its own (where an operating system is not present, etc) ... then KillDisk is an excellent utility.
*. Platform Independent file system eraser : Whether you have MS Windows, GNU/Linux, free BSD or Mac OSX , etc file systems... it doesn't matter to KillDisk it'll treat them all the same :).
*. Supports IDE / ATA / SATA / SCSI hard disk drives (including USB and SSD drives).
*. Erase data on both used and free space. If you only want to erase the free space then use the "Wipe" button. To completely erase the drive/partition, etc use the "Kill" feature.
*. Advanced scan methods for NTFS and FAT file systems.
*. Easily create a boot-able environment (a "DOS" type environment) using media such as: HDD, USB, Floppy, CD/DVD.
*. Wipes out deleted MFT and ROOT system records.
*. The free version supports only single-pass zero method which is pretty decent for most.
But for the best secured deletion ... you'd wanna consider purchasing the Professional version which includes few advanced features such as: user defined methods (including random numbers, characters, passes, etc) and few other Army and Government approved secure deletion algorithms, etc.
*. Erases both file system data and even boot sectors! (so always think twice before using :D).
These are just a few of its main features to mention. Although I only used it under Windows but as mentioned, it comes with a GUI tool that lets you easily create a boot-able disk drive. It however did not detect my GNU/Linux partition as a Ext4 file system but it can delete data nonetheless!.
And also remember, if you have a dual-boot environment with GNU/Linux and only want to wipe the GNU/Linux partition/s, then first make sure to remove the GRUB boot-loader. Otherwise you might not be able to boot-into MS Windows afterward (as long as you have the Windows installation CD/DVD ... this should be fixable most of the time, but just keep that in mind anyway).
So, if you're looking for a free, platform independent disk drive eraser that suits both individual and professional needs then KillDisk is certainly a pretty powerful application. But please be aware that if you want the best possible results then perhaps you might wanna purchase the "Professional" version + after using it, you will not be able to recover data ... so use it with caution. Good luck.
Get it from this KillDisk Home page.