When do I need to use Eraser?

You should use overwriting every time when removing data from your drive. You do not need to overwrite data which you think is neither secret nor sensitive, but there is no harm in overwriting everything.

However, there are some cases where overwriting may not be suitable or may have side effects. These cases are discussed in the following section.

You may also want to erase the unused disk space on your drive regularly to get rid of the remains of temporary files created by applications and other information that may have been stored on your disk. You can use the Scheduler to run the task when the computer is not in use – overnight, for example.
<h2>Exceptions</h2>
<div>
<ol>
<li>Compressed Files/drives
You cannot erase files compressed at the file system level (file compression requires a file system that supports it such as NTFS). Files compressed with an external application, such as ZIP files, can naturally be erased.</li>
<li>Encrypted Files
You cannot erase files encrypted at the file system level encryption requires a file system that supports it such as NTFS). Files encrypted with an external application, such as Pretty Good Privacy (PGP) or AxCrypt, can however be erased.
As the data is already stored in unreadable format, erasing is not required, but usually increases security (prevents recovery if the key is compromised, for example)</li>
<li>Encrypted Drives
You may wish to erase the free space of encrypted drives (such as that of TrueCrypt) for the same reasons as those in Encrypted Files. This will work however as the encryption is transparent to Eraser.</li>
<li>Network Drives
Erasing files over the network may work; however it will more likely fail to securely erase your file as data is modified through the network protocol and the semantics required for erasure may not be present. Furthermore, you are very likely to saturate the network, which is very inconsiderate.</li>
<li>Floppy Disks
You can erase data on a floppy disk as if you were erasing a hard disk. However, if you have stored sensitive data on a floppy disk, you may want to consider physically destroying the disk using another method, such as burning it.</li>
<li> CD-RW, DVD±RW, solid state drives etc
These drives have a limited rewrite span and thus you may want to reserve the unused space erasures for emergencies. Also, a single pass is sufficient for eliminating all traces of files as they are not magnetic media. If your media is cheap (e.g. CD-RW) you may consider crushing the disc.</li>
</ol>

<div>

Unless you are writing to media which have limited life span, for example USB keys, CD-RW, DVD±RW, solid state drives etc.

</div>
</div>