We’re rewarding the question askers & reputations are being recalculated! Read more.
249

Because of the following reasons: Performance - it takes up resources destroying files. Imagine an application that uses hundreds or thousands of files. It would be a huge operation to securely delete each one. Extra wear and tear on the drives. Sometimes the ability to retrieve a file is a feature of the OS (e.g. Trash, Recycle Bin, Volume Shadow Copy). As ...


161

Modern SSDs use a technology called SED which allows instant erasure. It works by transparently encrypting the entire drive and keeping the key on the drive. ATA Secure Erase is then implemented by wiping the key alone, which renders the rest of the data immediately unreadable (assuming of course that it has been correctly implemented on that particular ...


108

Instead of another "You are wrong because" answer I'd like to take a slightly different approach: Early computer OS's were written by programmers for programmers. Any one who programs and knows what pointers are understands that "deleting" a pointer doesn't delete the thing its pointing at: they are separate. That doesn't mean that delete doesn't actually ...


104

Summary: it was marginally better on older drives, but doesn't matter now. Multiple passes erase a tree with overkill but miss the rest of the forest. Use encryption. The origin lies in work by Peter Gutmann, who showed that there is some memory in a disk bit: a zero that's been overwritten with a zero can be distinguished from a one that's been overwritten ...


96

It doesn't have to be corrected because it's not a fault. The pointers to the file are deleted, and the area the file occupied is marked as free space. The drive then overwrites this area in its own time. It's purely there to save wear and tear on the drive. After all, storage devices (especially SSDs) have a limited number to times they can write before ...


75

You seems to have a wording problem with the delete term and a wrong expectation about what the functionality should do. You can check the simple definition on the Merriam-Webster website: delete: to remove (something, such as words, pictures, or computer files) from a document, recording, computer, etc. The goal of the delete feature is to remove the ...


72

Yes. If you do a normal format, the old data can be recovered. A normal format only deletes/overwrites a tiny bit of filesystem metadata, but does not overwrite all of the data itself. The data is still there. This is especially true on SSDs, due to wear levelling and other features of SSDs. The following research paper studies erasure of data on SSDs: ...


51

Data destruction is a technique of last resort. If you are planning to use a new storage device, you should use full disk encryption. This allows you to either destroy the encrypted master key or simply forget the password, effectively rendering all data unrecoverable, despite no data actually being wiped. Encryption is a solution for both solid state and ...


45

Quick-formatting a hard disk simply erases the filesystem's structures and tables and writes new ones in place, giving the illusion of a brand new disk. Old data is simply overwritten as and when needed, but it still remains on the disk. File carving utilities can go through the disk data and recover fragments of files, then stitch them back together without ...


43

To quote the ISM (Australia's military standards for cyber security). Security Control: 0359; In flash memory media, a technique known as wear levelling ensures that writes are distributed evenly across each memory block. This feature necessitates flash memory being overwritten with a random pattern twice as this helps ensure that all memory blocks ...


38

You have to stop thinking about this on the file level. For a storage device, all that matters is the sector. If one sector on a hard drive* is overwritten, the data in it is gone for good. There is no known way to retrieve it even with "powerful software", and there is no need to overwrite the same sector multiple times. Modern hard drives encode data in ...


31

There is a well-known reference article by Peter Gutmann on the subject. However, that article is a bit old (15 years) and newer harddisks might not operate as is described. Some data may fail to be totally obliterated by a single write due to two phenomena: We want to write a bit (0 or 1) but the physical signal is analog. Data is stored by manipulating ...


31

As quoted from this page: Secure erase overwrites all user data areas with binary zeroes. Enhanced secure erase writes predetermined data patterns (set by the manufacturer) to all user data areas, including sectors that are no longer in use due to reallocation. This sentence makes sense only for spinning disks, and without encryption. On such a disk, at ...


28

I would still recommend using secure delete in your scenario. Should your machine be compromised when you are logged in (malware etc), full disk encryption will not protect you from a undelete operation via C&C malware for example. SSDs have problems erasing files but a number of manufacturers provide utilities for their drives to securely erase a file ...


23

How deep down the rabbit hole do you want to go? For OS level malware: Sure, wiping the hard drive is fine. To be extra sure, overwrite the entire hard drive with 0s manually using a secure erase tool. For hardware/firmware level malware: Well... no. These things live in the actual firmware of your PC and will reinfect your hard drive every time. For ...


22

First of all (just to be on the safe side) verify the file isn't in the Recycle Bin. If it is, choose Restore and of course shred the recovered file (or maybe you can shred it while inside the Recycle Bin). If the file has been "truly deleted", recover it using an undelete tool such as Piriform's Recuva, then shred it for good. Note (suggested by Chris H): ...


22

Next time you're about to put sensitive data on a flash drive, consider encrypting it first! Strongly encrypted data is useless without the key, and if you securely erase the drive first, all that will be left is an occasional sector of such encrypted data surviving due to wear leveling. If you're still unsatisfied by this technique because there's a small ...


18

Overwriting the data is either insufficient or useless, depending on how things are done internally by the device itself. Flash memory has a limited life, expressed in terms of read/write cycles. To sum it up, you can have one block of data full of zeros; bits can be changed from zero to one individually, but the reset to zero can be done only for a complete ...


18

The reason you write '0' instead of '1' has to do with the way magnetic storage encodes the 0 and the 1. a long explanation of it can be found on Wikipedia under Run-length_limited. In short RLL is the methodology used to store the '1' and '0' and it is more complex than just to store the bit values themselves. On a side note to make the drive more like it ...


17

There isn't much you can do about it besides deleting your Facebook profile (different from deactivating it - though I'm sure in both cases nothing is really deleted). As for how Facebook got your number - they have a feature in their mobile apps which allows people to upload their contacts to Facebook - if many of your friends had this enabled (and the app ...


17

A quick check at amazon.com shows 64GB USB drives in non-designer cases go for about $20. Less if you buy in bulk. Since you want "quick and efficient" lets factor in the time needed to overwrite the drive at least twice, and maybe running a drive scanner to verify the erasure. And then remembering to do it each time. A quick check of homedepot.com shows a ...


15

A paper from 2011 by four people from the University of California, San Diego writes in section "3.2.1 Built-in sanitize commands": Of the 12 drives we tested, [...] Eight of the drives reported that they supported the ATA SECURITY feature set. One of these encrypts data, so we could not verify if the sanitization was successful. Of the remaining ...


13

The problem with deleting files is that the file data is just one small part of what really gets saved onto your disk. On a modern filesystem there will be lots of metadata and other artifacts scattered around the disk: Journal entries on journaling filesystems, e.g. NTFS, ext3, ext4. Search index entries. Prefetch / superfetch cache entries. Shadow copies. ...


13

Tl;dr: Because you can never trust all storage drives to securely wipe themselves, you must plan as if none of your drives can be securely wiped. Placing a dependency on the type of media is not the right way to approach the problem, because the technology is always evolving and changing, and you can never be in 100% control of all IT spend. Remember that ...


12

The 7 and 35 passes very probably come from the paper "Secure Deletion of Data from Magnetic and Solid-State Memory" by Peter Gutmann. There, he described various overwrite patterns targeted at specific hard drive write encodings. However, the paper, and the 35 passes, are now obsolete, as they were for old hard drive technology, as even the author readily ...


11

1) With modern filesystems, there is no more concept of securely deleting an individual file. It might have been copied around, snapshotted, written to a different location upon editing, etc. 2) With modern drives, there is no deletion / wipe without confirming it. Some drives have had a Secure Wipe command flat-out lies to you, returning immediately while ...


11

UPDATE: Upon looking back it looks like using random data is not really necessary as a successful platter-level 'previous state' attack on a zeroed drive has yet to be proven possible in a real-world attack. I've left the references below for posterity and because it does technically work fine if you're using random data, but given that just using 0s is ...


11

You are seeing a consequence of the ongoing war between binary and decimal systems. Namely, 210 = 1024, which is close to 1000. Hence a widespread habit of saying "kilobyte" (as in "1000 byte") for a quantity of 1024 bytes. When we go to megabytes and gigabytes, the deviation increases: 220 = 1048576, and 230 = 1073741824. Therefore, if tool A displays a ...


11

It can be. Generally speaking, programs while running don't tend to wipe out their data (they do, after all, tend to need it), and any process with the ability to access other programs' allocated RAM can, in fact, read it. This is how, for example, the recent spate of big box store hacks were able to leak so much credit card data -- the attacks were carried ...


11

For performance reasons. Deleting the file from the index, and declaring that the zone where the file was is now free and can be re-used is far more efficient that erasing all data over that zone.


Only top voted, non community-wiki answers of a minimum length are eligible