All I found via Google was outdated advice. In neither the Wordpress.com nor Wordpress.org (i.e. installation on own domain) can I find any option in the "security" or privacy settings aside from the one setting of "Search Engine Visibility", i.e. "Discourage search engines from indexing this site".
Basically I want to either temporarily deactivate my blog (i.e. make it completely inaccessible) or make its - previously public - content private. Is that possible as of April 2013 or in Wordpress 3.6? (Which I have installed right now.)
I hope this question is within the scope of the Wordpress questions allowed here.