Hopefully, most/all people know that simply clicking “delete” on your computer is not going to delete the files. Erasing a file simply erases the file system entry, leaving the actual file intact and accessible to others if they have the correct tools and know-how.
To combat this, various “secure” deletion programs have been created: eg shred and secure-delete (srm) etc in the Linux/UNIX world, and programs such as Eraser, Freeraser, Blank and Secure and DP Shredder (and others) for Windows operating systems.
Unfortunately these tools are not a cure-all. If someone has physical access to your laptop, a skilled technician can fool these programs and make the computer to spew its guts. Just look what the NSA and GCGQ did to a Guardian computer believed to be carrying details of what NSA whistleblower Ed Snowden had told them. Just check out what staff members of the Guardian newspaper had to do under the watchful eyes of NSA/GCHQ operatives to ensure no nasty ones and zeroes got out there to knock Western Civilisation down onto its knees.
Many folk in the computer security community think this was “security theatre”… the NSA/GCHQ experts did stuph that was in no way necessary, it just helped stop educated security guys from figuring out what bit of laptop needed to be trashed and what was trashed for no reason except for the daft notion of “obscurity = security”. Secirity experts will have talked with their expert buddies to find out what they thought as they watched the computer dismantled and buggered-up beyond recognition.
Anyway, have the NSA/GCHQ forgotten that mantra that is beaten into them at school “back-up, back-up, back-up”. Who says that the files on that laptop were unique? I seem to remember that a number of newspapers around the world were publishing details of this story… do NSA/GCHQ held the only copy of the intel? That is a stupid idea. If I was given a story whose details and proofs were on a disk, I would send copies to everyone, to be published if I slipped and fell horribly in the shadow or I disappeared one night never to return.
Bloody stupid intelligence service. Their #1 secret = there is no intelligence regarding their intelligence. Because they have none. Now let’s go drive off a cliff somewhere. Orders is orders, innit?