Safer Internet: Offline: Erasing Your Device


  • pencil+ Do you want others to access your files on a donated / discarded computer, phone, printer or other device?
  • + Your files may still be accessible after normal delete -- unless encrypted, or stored on SSD (solid state drive) instead of regular (spinning) hard disk
  • + Deleted / hidden information in a file might be recoverable
  • - Different meanings for "delete/erase"
  • - Have to remember to setup or check


Secure File Erasing

  • Even if you empty Trash / Recycle Bin, various utilities might be able to recover file content.
  • macOS: (≥ 10.10) use FileVault: erased file sectors are still encrypted -- thus unreadable; see Encryption section
  • macOS (< 10.10): Finder > Secure Empty Trash
  • [2] macOS (< 10.10): Disk Utility > (select drive) > Erase > Erase Free Space: number of times -- unused space from deleted files
  • [Refs:macOS]: "Disk Utility's erase free space feature"

[2] Erasing Apps

  • To remove not only an app, but also its settings, storage caches, etc.:
  • iOS: press down on app icon to enter move / delete ('jiggly') mode
  • tap "x" in upper left corner
  • popup: "Deleting (app) will also delete all of its data"
  • (press Home button to exit 'jiggly' mode)
  • To immediately delete related iCloud data:
  • iOS: Settings > iCloud > Manage Storage > (device) > disable old app
  • macOS: just dragging an app (from Applications folder) to Trash does not remove extra files
  • Use an app removal utility, e.g., App Cleaner
  • To find out how much storage is used on your device:
  • iOS: Settings > General > Storage&Cloud Usage > Storage > Manage Storage
  • macOS: [apple] > About This Mac > Storage

[2] Securely Erasing Device

  • ergonomicsSecurely erase drive before donating, discarding, recycling or selling your device; to be nice, re-install OS
  • iOS: Settings > General > Reset > Erase All Content and Settings
  • [Refs:iOS]: "How to erase your iOS device and then set it up as a new device or restore it from backups"
  • [Refs]: "How Do I Securely Erase My Phone Before I Sell It?"
  • Trigger auto-erase if lost or stolen?
  • iOS: Settings > Passcode > (passcode) > Erase Data -- after 10 failed passcode attempts
  • iOS: iCloud > Find My iPhone/iPad -- allows you to erase remotely
  • macOS: restart from another disk, e.g., Recovery Partition; Disk Utility > (select drive) > Erase > Security Options -- everything: are you sure?
  • [Refs]: "HowStuffWorks: 10 Things to Do Before You Wipe Your Computer"

[2] File Redaction

  • very funny redactedSome source files (e.g., .doc, .pdf, .jpg) can retain layers / versions of info, i.e., metadata, or track changes; it might be recoverable via copy/paste or tools; just deleting it or overlaying an annotation may not be enough!
  • So, omit sensitive info from files in the first place: content as well as metadata such as Author, Organization
  • or, save edited document or selected screen area as an image
  • or, copy/paste selected (non-sensitive) info into a simpler format, i.e., one that removes any hidden info -- or use redaction tools (next)
  • Remove photo metadata; e.g., phone location via iOS: Photo Investigator
  • Redact a .pdf or source document to remove sensitive info -- using proper tools, i.e., Adobe Acrobat Pro; otherwise, simple annotations / changes can be selected, copied, revealed
  • [Refs]: "Redacting with Confidence: How to Safely Publish Sanitized Reports Converted From Word to PDF" (PSA from NSA)