Can data that has been completely overwritten ever be recovered regardless of device unless it is an SSD? By completely overwritten I mean that if data is written to a device for 2 years continuously it is obvious that previous data is overwritten. So can the original data be accessed?

By devices I mean:

  • Harddrives
  • Android memory (which i think is eeprom)
  • iPhone memory

If yes, is his a solid fact (one which will remain true till the end of world. a fact which is as true as 2+2=4)?

closed as unclear what you're asking by S.L. Barth, techraf, Steffen Ullrich, tlng05, Gilles Aug 1 '16 at 21:53

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • You actually received pretty informative comments on your question yesterday which you appear to have dismissed since you still skip the specifics and ask about future possibilities. It is presently possible to analyze a hard drive and guess 2-3 layers of rewrite even though the data was effectively overwritten, so foreseeing if advancements in technology will make it possible to recover previous overwrites more easily and accurately is impossible. – Julie Pelletier Jul 31 '16 at 20:04
  • There goes your answer, such an hypothetical question can not have a mathematical answer such as 2+2=4, especially considering that what was taught as absolute facts when I was in high school about the electron and proton being undivisable had already been proven wrong back then. – Julie Pelletier Jul 31 '16 at 20:04
  • @JuliePelletier: do you have any sources for the claim about recovery after 2-3 overwrites? – WoJ Jul 31 '16 at 20:48
  • @WoJ: No, I gave a conservative comment on something I read a while ago since there is no way to give a valuable answer either way. – Julie Pelletier Jul 31 '16 at 21:10
  • So please do not mislead with such comments. The conservative numer is one pass (see for instance security.stackexchange.com/a/53264/6341 or the forensics wiki, or NIST recommendations) – WoJ Jul 31 '16 at 21:19

Current scientific belief suggests that information can never be created nor destroyed, so when you start talking about "until the end of the world," you need to understand that you are setting a markedly high bar.

Every device treats the process of overwriting existing data differently, so asking for the current state of affairs on a diverse set of devices with the level of certainty you seek is a daunting task. For some devices like EEPROMs, its rather reasonable to assume overwritten information is nearly impossible to recover. For others, such as harddrives, there's no particular guarantee as to which sectors an OS will use, so its plausible that data might not actually get overwritten, even with continuous use. That's why companies produce harddrive erasure tools which explicitly affect every sector on a disk.

From this question and your other question with equally vague details, bad formatting, and a tone that I would categorize as a bit hysterical, I would recommend you pause for a moment and develop what the industry calls a "Threat Model." This threat model is designed to capture the capabilities and intent of any adversaries you face. Once you have developed one, it may be easier to develop actionable questions for which the community can help you with. A Threat Model lets you recognize that there is a cost associated with security and lets you balance that cost in a rational manner. It's what lets you realize that while setting off a thermonuclear device over your computer will be highly effective at sanitizing the data, there are better ways to go about things.

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