Summary
By default, autocomplete is turned on for passwords on the Forms login screen. If autocomplete is turned on, a browser can asks users "do you want to remember the password for this site?" and then store the user's password for logging in in the future. You can disable this setting by editing the Login.cshtml file.
Note: Modern browsers are increasingly ignoring the autocomplete setting, so turning it off may not prevent the browsers from asking the users for their password.
Resolution
To turn autocomplete off for passwords on the Forms login screen:
<!--Enable this to prevent browsers from storing password
<div class="hidden">
<input type="password" />
</div>
-->
to
<div class="hidden">
<input type="password" />
</div>