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Anthony Cossey


Anthony Cossey - Fixnetix ltd

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Securely Delete Files on your Computer

08 December 2009  |  5310 views  |  3

There are times when you really want to make sure a file on your computer is deleted and can't be recovered by a PC expert, I am sure I don't have to preach about how it is really important these days to 'securely delete' your files.

Remember any leak of the data in your files with any financial records or personal information can of course lead you to being ripped off by a ID fraud type criminal. If such criminals can undelete files on your hard drive and access the content then your security has been badly compromised.

Also when you sell a computer, give an old computer to someone or indeed dispose of it, its important to securely delete all your data. There are BOOT CD's like DBAN which can delete everything from a computers hard disk, however the best method is to have the physical disk crushed by an expert company

Also ANYONE these days can be a deleted file recovery expert, there are free utilities for windows like "Recuva", which can restore nearly any file that has not been 'securely deleted', thus anyone can be a instant expert with one google search......Dangerous i am sure you will agree.......

However secure deletion is pretty easy to use. (Also i would encourage you to use recuva as way of getting files back that have been non securely deleted in error on Windows -- see here www.piriform.com/recuv )

What is secure deletion?
A very clever individual has worked out a way deleting a file securely from a computers hard disk using a a technique that overwrites the data over 30 times with random bit patterns. see here http://en.wikipedia.org/wiki/Gutmann_method

Also take caution when using these secure delete programs below as once the file is SECURELY DELETED its GONE FOR GOOD. 

The free windows deletion utility "ERASER" implements this GUTTMAN technique and is the only free way of making sure deleted files are REALLY deleted forever on Windows......download and install ERASER from the link below and make sure you turn on GUTTMAN deletion from the options.

You can right click on a file and ERASE it securely, you can also do this with the Windows Trashcan, where deleted files are stored for recovery (its the icon like a dustbin on your desktop. Also ERASER securely 'moves' files from one location to another by deleting the old locations file image.

You should note that if you are deleting a lot of files at once it can take a long time, i had to securely delete on a Linux system 16 gig (4 DVD's worth) of data and it took over 24 hours. However for single files and anything under 1 gig ERASER is quick enough.

Website & Download for Eraser

For mac users , you need to CAREFULLY follow this guide from Apple on secure deletion


To delete from the Linux command line Install the 'secure delete' package from your Linux vendor, this gives you a command line utility "SRM" or in some cases "shred" or "wipe"

To securely delete from the GNOME GUI follow this guide below

To securely delete from the KDE GUI follow this guide below

Hope this helps you out in some way.


Comments: (3)

John Dring
John Dring - Intel Network Services - Swindon 09 December, 2009, 15:35

I am sure I can search and find the answer - but why when you overwrite the data blocks, say just once, can the data be recovered?  I understand its not enough to delete the file pointer and links, but if you overwrite the data itself - its gone?  Why overwrite 30 times?

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Cedric Pariente
Cedric Pariente - EFFI Consultants - Paris 10 December, 2009, 10:31

The simple explanation is that it's like when you try to clean a dashboard. There is always some chalk remaining.

Concerning a hard drive you are also talking about polarisation. You leave a magnetic trace that can be recovered after a simple deletion.

You can assimilate the 30 times to the 30 times your hand goes on the dashboard to erase the remaining chalk on the sides. :-)

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A Finextra member
A Finextra member 10 December, 2009, 11:36

I tend to use the maxim, "I may be paranoid, but am I paranoid enough". The last time I upgraded to a new laptop, after deleting my financial data I also take the hard disk out of the old machine, smashed open the hard drive and poured used motorcycle oil into it.

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