I got to getting my notebook repaired (was broken for months, I am so not a road warrior) and one of the reasons it took me so long was reluctance to spend time on properly clearing private data from it.
As with backup this is one of the things that people tend to skip. But really if losing personal data is bad enough, getting it given away and ending up who knows where is kinda worse. It doesn’t help that there are many types of personal data and it can be hard to get rid of it.
Keep hard drive
The obvious and most reliable way to keep that data to yourself is make sure it never leaves. Taking out hard drive before giving computer away can be both easy temporary measure or (if computer not coming back) reliable way to be sure your data stays with you.
From there you can either destroy hard drive properly (fun! :) or keep it around for extra storage and such.
Delete private data
If you need to give drive away after all it gets tricky. Of course you can erase everything (really everything), but that can be unwanted for yourself or person that will need to repair/use/whatever your computer.
My checklist for removal of private data goes roughly like this:
- unlink and uninstall online sync tools, such as Dropbox;
- run private data cleanup in every browser present (most modern browsers have such function), uninstall them (if not part of OS like Internet Explorer) and delete profile folders to be sure;
- uninstall paid software and choose to not retain licensing information, if not given such choice – check registry for leftovers of such;
- run global search (Everything works nicely) for typical file formats (such as archives, documents and media) and delete anything private.
Make it unrecoverable
It is often trivial to restored freshly deleted data, or at least parts of it. To make sure the things you deleted stay that way you need to wipe free space thoroughly. CCleaner can do this, via Tools > Drive Wiper. Note that it can take hours, depending on amount of disk space to wipe.
Note that according to some tests it can be near-impossible to reliably and securely erase data from SSD, so account for that if you use such drive.
Check what you get back
Aside from being concerned about data copied from your computer it is not unwise to be also concerned about data being copied to it. If your computer was out of your hands, at the very least run a thorough antivirus scan after you get it back.
Thoroughly disposing of private data might seem like a drag, but it’s not something you need to do often and something you really need to do. If for some reason this becomes a common task for you, it might be more efficient to just keep data encrypted with TrueCrypt or similar tool.