Most of us obsess about retaining our data - we buy large hard drives, burn countless DVDs and protect it all with RAID controllers and UPS devices. What many people care much less about is making sure that discarded data is really gone. How many times have you thrown a dead hard disk in the trash, wiping a tear for your lost files? Did you consider that a person with sufficient technical skill may grab it from the trash, recover the data and make some coins off it?
Well, the issue of data destruction has been the center of much debate. Most people are already aware that deleting a file doesn't really erase it - it simply deletes the reference to the file in the disks directory (I'm talking about actually deleting, not moving it to the trash, which doesn't delete anything), while the data is still there, untouched. A file that has been deleted can be re-created simply by finding it's 1st sector, and creating a file entry that points to it. Once you delete a file, it can be overwritten by windows, as it the system creates new files. the new files might overwrite some or all of the file's original sectors, which are now marked as free, but these sectors can also remain untouched for years.
Some people will go the distance, and actually format the hard drive before throwing it away, but this too is not sufficient. Restoring a formatted drive is more time consuming, but certainly possible. The US Department of defense probed this issue in the past, and produced a standard, known as DOD standard 5220.22, that instructs exactly what to do to erase data properly. Later on, there was some debate as to this was safe enough. Some expert claimed that you would need to overwrite the data over a dozen times, and that has been misquoted repeatedly in the press since then.
Security experts are very much concerned about erasing data securely. A company cannot risk it's commercial data falling into the wrong hands simply because somebody was too lazy and took a shortcut with the disk. Same goes for other types of media - DVDs, backup tapes etc. Even a lost cell phone could present a serious security breach, as it could include phone numbers of sensitive customers, sensitive emails or meetings etc. I would like to take this opportunity to debunk some myths about data destruction.
1) Hard drive demolition derby.
• A common method of destroying disks, by punching a hold through them, or banging them strongly with a hammer is far from secure. It's not easy to recover in this condition, but it's certainly possible.
• With modern IDE and SATA disks, using a 5220.22 secure erase software is very safe. there's no need to overwrite everything dozens of times. The need for that kind of rewrites referred to some very old MFM drives.
• Using software erasure is pretty slow, but it can be done unattended, so setting up some dedicated old computer for that is pretty easy. Just make sure no one tries to steal the old drives from that station.
• A very effective way to destroy a disk is to take it apart, and separate the plates from the other components. Dumping the plates in a different trash facility makes it pretty much impossible to recover.
• There is a technique that allows data recovery off a drive in almost any condition, but that process is so lengthy and expensive, that most experts would consider it irrelevant. Recovering data from a disk that was physically destroyed would cost so much time and money, that even government agencies don't bother with it.
• Take care to monitor old computers - many times people upgrade the disk and don't think of giving the old disk back to the IT group for sanitation. Some even take the old disks home, thereby exposing the company to huge risks. This also goes for computers that are being retired - don't sell them to 3rd party companies without either sanitizing them, or making sure that the buying company commits with a contract to do this to ALL disks.
2) Other media types:
• Recovering data off other media types, such as tapes, CDs, floppy's etc is rather easy, but these media types are also much easier to destroy. Even a little heat can totally kill an optical disc, and a strong magnet can kill a tape almost instantly. I would, however, recommend a process is used for this - don't just break a CD, and don't pop it in the oven - use a CD shredder, which costs very little these days.
• Users often overlook CDs as a potential security risk, and often throw them in the trash. A security officer would be wise to issue a recurring reminder to all employees to collect discarded CDs and DVDs and have the IT or security department dispose of them securely. This goes not only for data disks, but also software - if someone finds and uses an old copy of windows for illegal purposes, with the company's serial number, it could lead back to the company and carry legal repercussions.
• Many people carry around USB drives to take a file or two back-and-forth from/to home. This is a big risk as these drives rarely get formatted, and often are lost. I would recommend any organization introduce a security mechanism to block such devices altogether, or at least control them with a policy (for example, require to have them signed by corporate security before they are allowed in)