When my Mac locks itself due to inactivity, or because I've switched to the login screen (without logging myself out), what actually changes? For example:

  • Is access to data on my hard disk affected? (I realise that unless full disk encryption is turned on it will always be possible for someone to read it directly from the disk - so I'm wondering if any more minor safe guards are put into effect).
  • Is access to data in my Mac's RAM affected?
  • Precisely how is access to my running programs affected? (eg: if my Mac is unlocked anyone could use Safari's saved passwords feature to log into various web services in my name; is this possible when the Mac is locked? If not, why not?)
  • How easy is it to bypass the lock screen, and what would this involve?
  • What IS the lock screen, when you get right down to it? Is it just a cosmetic GUI feature and a minor inconvenience to would-be bad actors? Or does it actually invoke deeper protections within the operating system?

The only practical benefits of locking a Mac that I have been able to positively identify are:

  • Preventing someone snooping while the user is away from their machine.
  • Acting as a system-wide event for interested processes (eg: 1Password and Keychain know to lock themselves when the computer is locked).

Please note that I'm looking for a technical (and ideally detailed) answer, as more general details are readily available online.

  • Note that a Mac's password lock can potentially be hacked with tools online. – owlswipe Jun 29 '16 at 1:21
  • @JohnRamos Can you expand on that, or link to something which does? – Subject22 Jun 29 '16 at 1:22
  • Certain tools (for a price!) can be loaded on to flash-drives and plugged into Macs, enabling a hacker with physical access to your computer to unlock a Mac (or PC). I will not go into further detail on specific services here, as that seems foolish and naïve. You should be able to find then online yourself, but I very very much discourage their use. Such tools are usually branded as tools that "unlock your Mac or PC if you forget your password." – owlswipe Jun 29 '16 at 1:24
  • Sure. I'd be interested to know how such hacks work though, and what the security implications are for the lock feature. I'm not worried about my computer getting broken into - I'm just interested in understanding the ins-and-outs of the feature. Thanks for your comment! – Subject22 Jun 29 '16 at 1:27

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