(via www.ubuntugeek.com)
Deleting a file or reformatting a disk does not destroy your sensitive data. The data can easily be undeleted. That’s a good thing if you accidentally throw something away, but what if your trying to destroy financial data, bank account passwords, or classified company information. In this article you will learn number of tools(Shred,Wipe,srm, smem,sfill,sswap,DBAN) to delete files securely in GNU/ Linux