I still see people quoting the Gutmann 35 method. It was never intended to use all 35 wipes on a single hard drive. Gutmann designed the 35 wipes to use multiple methods in cases where you don't know what type of drive it is, but for any known drive, only a subset were supposed to be used. That being said, it's pretty well established at this point that a single random write is sufficient to make all data unrecoverable. The National Institute of Standards and Technology says, "[F]or ATA disk drives manufactured after 2001 (over 15 GB) clearing by overwriting the media once is adequate to protect the media from both keyboard and laboratory attack." The Center for Magnetic Recording Research says, "The U.S. National Security Agency published an Information Assurance Approval of single pass overwrite, after technical testing at CMRR showed that multiple on-track overwrite passes gave no additional erasure." https://en.wikipedia.org/wiki/Data_erasure#Number_of_overwrites_needed Write et al. performed their own tests and found that a single overwrite was sufficient. Wright, Craig; Kleiman, Dave; Sundhar R.S., Shyaam. Overwriting Hard Drive Data: The Great Wiping Controversy. In R. Sekar, R.; Pujari, Arun K.. "Information Systems Security". Information Systems Security: 4th International Conference, ICISS 2008. http://link.springer.com/chapter/10.1007%2F978-3-540-89862-7_21 More here: http://dkn255hz262ypmii.onion/index.php?topic=99520.msg699299#msg699299 The most important feature of a random overwrite is to do the whole disk, not individual files. Files can be written to multiple locations of a disk, and overwriting an individual file only writes over its last location. You also need to use a tool that is not running on the host OS. The host OS usually reserves blocks which won't be overwritten by any tools running on the host OS. You need a bootable program like DBAN. Run the "nuke" option with 3 writes (2 random, 1 with zeroes) and the data will be unrecoverable. Then reinstall the OS and use full disk encryption so this isn't an issue in the future.