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Dangers of selling off your old hardware
This is just a story. Mr.X got some money and decided to buy a hard disk with more storage capacity for his computer. A man from the computer shop had installed the new hard disk, and installed the operating system on the new disk. Mr.X deleted the stuff on the old hard disk and decided to sell off his old hard disk through an auction site on the internet. Somebody called Mr.Y from a foreign country bought the hard disk.
After some days things started happening. Mr.X could not logon to his email account. Somebody else was contacting his relatives from his email address and asking for money pretending to be Mr.X involved in an accident in a foreign country. Somebody posted compromising photos of Mr.X along with personal details at many sites on the internet. The life of Mr.X was ruined for a long time.
Here is an explanation of what could have happened. Mr.X in his haste must just have used cntrl A in each drive and the delete key to delete the contents of the drives in the old hard disk and ended up with emptying the recycle bin. Ordinary deletion does not remove the actual contents on the hard disk, but only deletes the filename and changes flags to show that the space occupied by the deleted file can be overwritten by new data. Hence the deleted contents can be retrieved by using certain software (Some of these are available for free). Some examples of such software are pc inspector (www.pcinspector.de) ,smart undelete (www.smartundelete.com) etc. Some of these software can extract deleted data even from formatted drives. The procedure consists of connecting the drive to a pc running the program and scanning the drive and creating an image if problems arise. Some of the data retrieval programs can retrieve old photos and data from memory sticks used with digital cameras and also from cellphones running on certain os's. If cost is not a concern ( as with governmental agencies) there are certain forensic tools which can analyse raw data (0's and 1's) from damaged disks and produce lots of useful data.
Mr.X had used his computer for online banking, online credit card transactions ,for preparing his tax returns, for storing his personal photos and other files . Mr.Y or whoever bought the old hard disk from Mr.X must have used similar data retrieval software to get the personal details of Mr.X from the hard disk.
Mr.X could have used one of the many software available which overwrite the data instead of simply deleting a file. Some examples are eraser(www.tolvanen.com), dban (dban.sourceforge.net). The software 'eraser' can be set to overwrite the entire hard disk many times with pseudorandom data. 'dban' is a boot-up floppy/cd which can securely wipe a hard disk.
But overwriting the data need not be the complete solution, though if done properly, it might defeat simple/casual data retrieval methods. An interesting paper is available at (www.usenix.org). Another approach is encrypting the contents of the hard disk. Some examples of encryption software are (www.truecrypt.org), (axcrypt.sourceforge.net) etc. But do remember that when the unencrypted documents are opened for editing using some software like word, the software might create temporary files which contain data from the document. Therefore even after encrypting and deleting the original document sometimes the temporary files can lie around on the disk (especially in the case of a crash). Encrypting the whole hard disk is quite useful.
A combination of the two methods might be useful when selling your old hard disks.
When selling your old digital camera and you cannot overwrite the memory using your computer, a useful method is to just overwrite the memory manually by taking arbitrary non-controversial pictures one after the other overwriting the memory again and again till you are pretty much satisfied that the old pictures have been written over.
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