Shred your dig­i­tal doc­u­ments

Pro­tect your pri­vacy: de­stroy your data, don’t just delete it

Mac Format - - IMPROVE | SYSTEM -

‘Delete Printer’, ‘Delete User’, ‘Delete Re­minder’. Th­ese are all things that your Mac will do, and they’re all things you need to do from time to time. But there’s one no­table ab­sence, both from the list and from OS X as a whole – nowhere in the op­er­at­ing sys­tem does Ap­ple so much as men­tion specif­i­cally delet­ing files. And files, more than any­thing on that list, seem like a strange thing to leave out since we delete them all the time – or at least, we think we do. Re­ally, we’re more used to the idea of ‘Move to Trash’.

That’s why in this tu­to­rial we’re go­ing to look at what this means for you, your files and your pri­vacy, and how you can use OS X’s built-in tools to keep your dis­carded data safe from pry­ing eyes and ma­li­cious al­go­rithms.

First, it’s help­ful to un­der­stand what hap­pens when you click ‘Move to Trash’. That lan­guage is a near-per­fect de­scrip­tion of what goes on in the back­ground: the se­lected files move to the Trash folder. That’s it. No files are deleted, no data is erased, and no disk space is freed up; the files are sim­ply re­moved from their orig­i­nal lo­ca­tions and placed in a spe­cial folder in your user di­rec­tory: ~/.Trash. You won’t see that folder in Finder be­cause it’s hid­den by de­fault, but click­ing the Trash icon in the Dock opens a spe­cial win­dow pointed to it. From there, you can see ev­ery­thing you’ve moved to the Trash, drag files out to re­cover them, or click the Empty but­ton.

This is where things get more com­pli­cated. Once the Trash is empty, you can no longer see the files it con­tained, but they aren’t ex­actly gone. In the in­ter­est of speed and re­duc­ing disk wear and tear, emp­ty­ing the Trash does as lit­tle work as pos­si­ble. Un­der the hood, in fact, only one thing hap­pens, at least in the case of hard disks: any file sys­tem links to files in the Trash are re­moved. That means that the

Even after you empty the Trash, your data still ex­ists on disk for at least a lit­tle while

un­der­ly­ing data is dis­so­ci­ated from the names and par­ent fold­ers that used to lead to them, mean­ing they don’t ex­ist in a par­tic­u­lar place or with a par­tic­u­lar way to be iden­ti­fied. How­ever, though you won’t find them eas­ily, they do still ex­ist on your hard disk – or they do for at least a lit­tle while.

After the links to a block of data have been re­moved, it’s treated by the file sys­tem as un­used stor­age, which is why delet­ing files frees up disk space: when it comes time to store a new file, the space taken up by an un­linked (‘deleted’) file is reused. When this hap­pens, the data that made up the deleted file is fi­nally de­stroyed, over­writ­ten by the new file’s data. De­pend­ing on how large your hard disk is, this could hap­pen after a few seconds, a year or never, which means that the data mak­ing up a deleted file could linger for quite some time be­fore be­ing truly erased.

The fact that emp­ty­ing the Trash doesn’t wipe out your data im­me­di­ately can be good or bad de­pend­ing on cir­cum­stance. It means that you can some­times use the lin­ger­ing, un­linked data (called ‘data re­ma­nence’) to re­store an ac­ci­den­tally deleted file, but it also means that a thief could po­ten­tially ac­cess per­sonal in­for­ma­tion you thought you had deleted, or that re­selling an ex­ter­nal hard disk you thought you had erased could ex­pose your pri­vate data to its new owner. How­ever, OS X does in­clude easy-to-use tools to re­move data se­curely so that it can’t be re­cov­ered.

It’s im­por­tant to note that while th­ese tools are ef­fec­tive on hard drives, SSDs use a more com­pli­cated process to han­dle dele­tion, which makes the tools cov­ered here largely in­ef­fec­tive (Ap­ple even dis­ables some of them for SSDs). If you have an SSD, FileVault en­cryp­tion is a bet­ter way to pro­tect your data, but make sure you read up on what you’re get­ting into with it. Nathan Green­stein

The Trash is just a spe­cial hid­den folder in your user di­rec­tory, ac­ces­si­ble via the Go to Folder di­a­log.

With some Ter­mi­nal knowl­edge, you can even cre­ate and delete files right from inside the Trash.

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