Are Your Files Really Deleted?

You've selected your file and hit the delete key, and then you've gone to the recycle bin (or trash can) and emptied it. Your file has now entered the world of electronic oblivion, right?

Not so fast. Every single piece of your data is still there. Obviously, this is good news if you accidentally deleted a file that you now want back, but it not good if you are planning to sell or dispose of your computer and do not want your personal information in the wrong hands.

To understand this, your hard drive is divided into small sectors. When you save a file, it places it in one of these sectors. If it is too big for one sector, it will fill the first sector, and at the very end will be code telling it where to look for the next sequence of data. Very large files may fill tens or hundreds of sectors. The file system in your operating system (Windows, MacOS, Linux, etc.) contains a list of the files saved and where to look for the first sector of the file. When you open a file, the computer looks in the file system for the first sector, loads that sector, and then continues the process with each sector the file is using.

At the very beginning of each sector is a single bit that tells the computer whether or not it is allowed to write data into that sector. When you empty the recycle bin, it simply deletes the reference to the file in the file system and changes all these bits so that the computer knows it can write new data into that sector. However, the data is actually still there! Over time, much of it will eventually be written over by new files, but until the computer decided it needs that sector for new data, your old data will still be stored there.

However, you can make sure your files are actually gone. If you are planning to sell or dispose of your computer, I would recommend using the program CCleaner. The free version contains a Drive Wiper. Once it opens, click on tools on the left side, and then select drive wiper. Choose to wipe the free space (wiping the entire drive requires taking the drive out of your computer and putting it into another computer), and then choose the security level: the number of times that the program will write junk data into each empty sector. A single pass will be enough for most purposes, but if you have highly-sensitive data, you may want to choose more passes. Then, select the drive you want to clean, and click Wipe. The process will take a while, but the protection you will receive is definitely worth it.