keithfromkeighley wrote:
Hi,thank you for your input,I do not use an SSD and have found a file shredder that does the job well.
Be aware that due to the nature of hard disk sector replacement, file system optimizations, application file handling, your data could exist on the disk after you perform your shredder operations.
hard disks can decide to replace a sector that is starting to report too many read errors. Someone with sufficient skill can recover data from these replaced sectors. If your data is in those sectors it can be recovered.
The file system may decide to defragment your file, which will leave the original storage unshredded.
A Fusion drive will first write a file to the SSD, then later move the file to the hard disk. The original storage on the SSD will be unshredded.
An application that is processing your data may use cache files, and it is very common for an app to write the modified file data to a new file, then rename the new file to the original name. The rename operation will release the original file contents unshredded. In fact OS X has a file system call that makes this approach trivial for applications, so it is frequently used.
If you have sensitive data on your system, you should be using System Preferences -> Security -> FileVault (make sure you do not loose the encryption key). Then deleted files are just a bunch of random bits, as are any intermediate copies and remapped sectors.