如何将你硬盘中的数据永久删除
根据纽约时报的一项基础隐私调查表明，人们在硬盘中数据的清除上存在着普遍的错误认识。绝大多数的人们并不知道仅仅删除文件是不够的，因为这样做并没有真正的将数据从计算机上清除干净。调查还发现，事实上仅有33%的二手硬盘将数据清除干净。在你想将硬盘丢弃或卖掉之前最好先确定硬盘是否还存有任何有关隐私的个人数据。如果你想通过格式化或数据粉碎软件彻底的清除数据，那么这篇文章可以给你提供帮助。
当你删除存储在计算机上的文件时，这些数据并没有真正移除，它们的信息被保存在操作系统可以查询到的目录中。当你删除文件时，实际上仅仅是将文件从文件夹中移走，并且将这部分区域标识为可写入新数据。因此，这个区域在被新的数据覆盖之前，原始数据都是可以被还原的。这就是所有数据还原软件的工作原理，根据目录还原那些已经删除的数据文件。完全清除数据的唯一方法就是覆盖它。你可以通过格式化硬盘或是可以在硬盘中填充随机数字的数据擦除软件来实现这个目标。
两种主要的数据覆盖方法。
它的理论依据是1996年奥克兰大学计算机科学学院皮特.古特曼教授在第六届USENIX安全会议上所作的论文-《安全删除磁固存储器上的数据》。这是迄今为止最安全的数据删除方法------覆盖数据35次，使得任何还原数据的企图都是徒劳的。遗憾的是这种方法会耗费相当长的时间。
这种方法是美国国防部《清理和消毒标准》中的一部分，这种方法仅仅需要覆盖数据几次，安全性没有古特曼方法高，但耗费的时间却相对较少。当然这覆盖数据的几次都是有讲究的，比如使用补码及随机数字来覆盖数据等。
当然，如果有人告诉您覆盖数据所需的最多次数，那么他一定在误导您。没人知道要多少次才够。如果您根本不想冒险，那么需要确保从未将任何重要内容加密地写入磁盘，并将它们直接解密到锁定的内存。别无选择。
Windows下如何彻底的清除数据
Eraser是一款免费开源的数据清除软件。操作平台，从DOS到 Windows 2003，支持单个文件，文件夹及整个硬盘的数据清除。这个软件提供了三种方式来覆盖数据，包括上面介绍的两种，还有一种叫“伪随机数据方式”。这种方法仅仅用在未使用过的区域和压缩驱动器上。
整个驱动器的数据清除
DBAN(Darik's Boot and Nuke)是另外一款免费开源的软件，它可以运行在几乎任何机器上，它可以清除你整个计算机上每一个硬盘上的数据，因此使用它要加倍小心。下载后刻录到光盘，重启计算机，输入“autonuke”。
终极永久删除方法
1、 将硬盘从计算机上拆卸下来
2、 拧开螺丝，打开外壳，暴露磁盘
3、 将它们敲成粉碎
你的数据安全了 
感谢Airate的关注，他所说的工具Secure Data Disposal联想的官方网站有下载，下载链接，但是没有说明其安全性高低，不过IBM出的软件我还是比较放心的。
同样感谢ihome提出的新方法，他提出的方法比文章介绍的方法更完美：
真正确保安全删除的方法
1，将磁盘扔到炼钢炉中融化
2，用火箭发射到太阳
3，用航天器将其扔进黑洞
让Heroes 中的那个人制造一个人工黑洞扔进去也不错。
未来欧洲核子中心也可能经营这个生意 ：：-）
PS:看来都是看hero看多了，我也在追这部剧集。
如何将你硬盘中的数据永久删除
According to the New York Times, a basic privacy measure that is often overlooked is the proper destruction of data on hard drives. An ongoing study by British Telecom says that most people don't realize that deleting a file doesn't actually remove the data from a computer.
In fact, the BT research found that only 33 percent of second hand hard drives had been completely wiped clean. To ensure your drive doesn't contain any personal data before you give it away or sell it, you need to reformat the hard drive or use digital shredding software if you want to completely eliminate all traces of data. In this post, we'll show you how.
When it comes to data stored on your computer, deleting files doesn't actually remove the data. File information is kept in a directory so that the operating system can find it. When you delete a file, all you are doing is removing it from the directory and flagging that part of the drive as being available for new data. Until that region is overwritten, the old data can be retrieved, in fact that's how you can recover lost data. It's also the way most file recovery programs work - they look for data on your hard drive that shouldn't be there according to the directory and restore it.
The only way to completely remove the data is to overwrite the contents of the hard drive. You can do this by formatting the drive, or using data wiping software that fills your hard drive with random data.
Two Main Methods of Overwriting Data
The Gutmann Method
Based on Peter Gutmann's paper "Secure Deletion of Data from Magnetic and Solid-State Memory", this method provides the best security. Data is overwritten 35 times with carefully selected patterns, which makes it unrecoverable. Unfortunately, it also makes it time consuming.
US DoD 5220-22.M
Based on the United States Department of Defense recommendation 5220-22.M, this method overwrites the data seven times. While less secure than the Gutmann method, it is faster.
Mac Users: Data Wiping Built In
Macs come with data wiping tools built into their systems. To securely delete a folder or file, all you need to do is move it to the trash can and from the Finder menu select 'Secure Empty Trash'.
Alternatively, the Disk Utility program 'Erase Free Space' scans your hard drive for unused space and securely deletes it to military (7 passses) or Guttman (35 passes) standards. You can find it in the Utilities folder.
Windows: Data Wiping by Selected File/Folder
Eraser is a free, open source program that works with Windows 95, 98, ME, NT, 2000, XP, Vista, Windows 2003 Server and even DOS. It uses carefully selected patterns to overwrite your hard drive several times and lets you select single files, entire folders or the entire drive to be wiped clean.
How to Use Eraser
Download and install the application. Once running, you'll be presented with a simple box that allows you to either schedule an erase, or do it there and then (on demand).
There are three ways to enter data into the list if you are doing it on demand:
1. Select files and folders in Explorer and drag and drop them to the list
2. Copy them to the clipboard and then paste them to the list
3. Use the New Task command in the File menu.
Note: If you use the New Task command, a window will appear allowing you to select unused space on a drive, a folder or a file to be erased.
After you have added the data you wish to erase to the list, you need to select the method of removal.
- The Gutmann Method (Default)
- The US DoD 5220-22.M Method
- The Pseudorandom Data Method
Using the pseudorandom data method, all passes will be random data, which is highly incompressible. This is the only method that should be used when erasing unused space or data on a compressed drive. The number of passes is user selectable from one to 65535.
Once you've selected the files/folders/drives that you want deleted, and the method of deletion, you can run Eraser. It will ask you for confirmation before it starts erasing so make sure you are certain you want to continue as this is your last chance to prevent data from being accidentally erased.
Data Wiping of Complete Drive
Another free open source program that runs on Windowsvirtually any machine, Darik's Boot and Nuke (DBAN) wipes the entire contents of every hard drive it finds on your computer when you run it, so be very careful.
Darik's Boot and Nuke ("DBAN") is a self-contained boot disk that securely wipes the hard disks of most computers. DBAN will automatically and completely delete the contents of any hard disk that it can detect, which makes it an appropriate utility for bulk or emergency data destruction.
DBAN is simple enough to use. Once you've downloaded the program, write it to a CD, DVD, or thumb drive, boot from that and enter 'autonuke' at the prompt.
The New York Times has an in depth article about DBAN that includes an interview with the author, Darik Horn if you are interested in further reading.
The Ultimate Permanent Erase
While these methods of data wiping can be useful for most of us; if you're uncertain about using them, there is one other option.
- Remove the hard disk from the computer
- Unscrew the casing, exposing the disks
- Smash them to smithereens
Your data now remains private. :)
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