Security Questions provides administrator configurable challenge questions for use during the log in and password reset processes. Think of it like most bank website logins.
Log In Process
If enabled, depending on the selected protection mode, the log in form is altered in 1 of 2 ways:
To just show the username field and a submit button. Once a user enters their username, the module searches for their account, and randomly brings back one of their security questions. They then need to provide the answer to the questions as well as their password for authentication.
To show both the username and password fields up front, then after validating the supplied username and password, the user is prompted with a randomly selected question they have answered.
Password Reset Process
If enabled, the user is required to answer a question before the password reset process could continue.
The user register form also gets a fieldset of questions so that the user can pick what question they want to answer and a textbox for their answer.
Once logged in, the user will see a tab on their account page called "Security Questions." This page lists the questions that they have chosen to answer, and provide a link for them to edit their answer.
This module is not intended to be a remote kill for a client's site. If that is what you need, take a look at killswitch.
What does Lockout do?
This module displays a generic off line page with a message indicating that the site owner should contact technical support. The idea being similar to cPanel's "suspended account" page. Additionally, this module should be used in a similar environment. For example, I build websites for clients and host these sites on my server. They pay me on a recurring basis for the hosting. If they become delinquent in payments and fail to respond to emails or calls, I use this as my last resort to get their attention.
How do I use Lockout?
While logged in as "User 1" visit the lockout settings page, Administration > Configuration > System > Lockout, tick the box and save. While set, one can still access the /user and /admin* sections. This will allows "User 1" to log in again and turn off Lockout.
Doesn't the core maintenance mode do the same thing?