secure deletion of data.

Secure deletion of data.
When did you last delete a file? Back when hard disks were measured in megabytes, it was common to delete files as soon as you’d finished with them, in order to free up disk space. In these days of terabyte-sized hard disks, however, it’s easy to accumulate huge archives of documents, emails, data files and program caches.

This can be a godsend if you need to dig out a reference from years ago. But this information could be a liability if it fell into another’s hands. For example: your email archive may contain login and payment details for online services; browser caches and system logs can reveal what you’ve been up to online, and even store private information that’s been displayed on a web page. The temporary files created by programs such as Word and Excel may also contain confidential data – even if it’s been removed from recent versions of documents.

Most of us understand the importance of wiping all these personal files before disposing of a PC, whether you’re passing it on to a friend, selling it or simply taking it to the dump. But deleting files doesn’t erase the sensitive data as permanently as you might hope.

If you’re unlucky enough to have your PC stolen, you might not even get the opportunity to erase your data. And it would be easy for a hacker to create malware that collects potentially valuable data from infected PCs.

Clearly, it isn’t realistic to try to keep your PC completely free of personal files. For sensitive files that you use regularly, it’s worth using encryption – a subject we’ll return to in a future How To. As a general rule, keep only as much private information on your PC as necessary, and regularly purge anything you don’t need.

This post goes into a lot more detail in the windows section:
http://my.opera.com/internetsecurity/forums/topic.dml?id=1126782

In linux use bleachbit > http://bleachbit.sourceforge.net/
to wipe all deleted data.