Your browser does not seem to support JavaScript. As a result, your viewing experience will be diminished, and you have been placed in read-only mode.
Please download a browser that supports JavaScript, or enable it if it's disabled (i.e. NoScript).
What others say is true. Most Linux installers have an option to overwrite data.
If you want to destroy data independently, Darik's Boot and Nuke used to be good, though it seems discontinued now. ShredOS looks like a modern alternative.