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I have been wondering for a while, since (for example on WindowsOS) logs are stored of user activity on the computer and can be retrieved later on by forensic experts easily. Can a user use an external hard drive or a USB storage device to install and run applications on it, which will not be technically stored on the computer's internal hard drive? Will the computer log the activity running on that external USB/HD?

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    To which logs are you referring? And generally speaking, the answer as with everything else is 'it depends'. While not true it is generally good practice to act (from a security perspective, not a user looking to recover data perspective) as if any non-encrypted data that has ever graced a given machine is recoverable. For the paranoid, ditto for encrypted. – Jared Smith Aug 22 '16 at 15:34
  • It also sounds like you're planning to move sensitive data to an unencrypted easily-stealable usb stick, bad move if I've ever heard one. – Jared Smith Aug 22 '16 at 15:36
  • generally speaking, lets stay you have some text files on the external hard disk, and you connect it to view theses files. if i open those files using a program that is installed the external hard disk, would the data be logged somehow (of the text files)? – user3676224 Aug 22 '16 at 16:03
  • @user3676224, that's a different question. No, the log files generally don't reveal the contents of the data files, usually only the file names. (An application crash log, on the other hand, might contain incidental data or even a full memory dump revealing all the data.) – John Deters Aug 22 '16 at 16:30
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The operating system of the computer (Windows, Linux, OS X, etc.) keeps its own logs of activity, and those logs are independent of the activity being performed. So whether you run a program off a local hard drive or an external USB drive, the OS of that computer will still log it in the same log it always uses. In Windows, these are kept in the Application Event log, and are visible to administrators of that machine. (If you're interested, you can go into Control Panel / Administrative Tools / Event Viewer and see them for yourself.)

A good security practice for a system administrator is to immediately forward copies of security events from the computer's log to a central collection server for backup purposes. That way, even if a hacker manages to get onto the machine and destroy the logs he or she finds there, the hacker won't be able to get to the copies that have already been stored elsewhere. The forensic investigator will then have information to help trace what's happened.

  • If a hacker manages to get onto a remote machine, it might not be too wild to assume he can get into the central collection server. Multiple copies of logs are a good practise. Sure, have a central collection, but also push the logs elsewhere. – theabhinavdas Aug 22 '16 at 16:33
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I'm going to piggyback on John Deters's answer. All major operating systems (Windows, Linux, OSX) keep logs of user activity for varying purposes, and they are stored in various locations.

With that in mind, if you don't want to have logs on your activity, check out an amnesic operating system like Tails. Tails is run as a live CD, only ever storing information in RAM which is erased on shutdown. This leaves little to no information for forensic experts to recover (unless they did something like a cold boot attack: https://en.wikipedia.org/wiki/Cold_boot_attack but this is largely impractical, especially if you have decent physical security).

Finally, remember that no operating system that communicates on the internet can be truly amnesic, because at some point it has to send data (encrypted or otherwise) through routers, servers, etc. Tails mitigates some of this by using Tor by default, but your encrypted traffic is still visible. Not to mention that the NSA can compromise tor traffic by controlling exit nodes.

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