In short, you can't. However there are programs that will make it difficult for overwritten data to be recovered. it all really depends upon why and what you need to remove securly. Eraser is a good program and will do the job admirably, you can probably find it on a few PCA disks if you have kept them. For most of us that is all that is needed. The only surefire method of destroying data from a hdd is to destroy the drive.
Belatucadrus thanks. I am using ultrawipe now. My query is how about the files I have deleted in the past,i.e. past few months for example ? Are they still on my hard disk & can they be retrievd by someone?
Items that are deleted are all recoverable until something else is written over them. In order to eliminate these files, open Ultra Wipe, click on "Advanced functions" In the new window, click the drive you want to clear and then select "Wipe free space". This will write several layers of random gibberish over any of these files, making recovery by anything short of a forensic lab impossible.
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