This is not part of the plugin.
You will need to make your own widget plugin following the instructions here: http://question2answer.org/plugins.php
In the part where you output the ads check the value from qa_get_logged_in_userid() - if it's NULL then the user is not logged in.
Thanks scoot;
Open qa-wa-layer.php (q2a-widget-anywhere-master plugin)
Go to line 83
Change the code with bottom
if ( $wid['position'] === $pos )
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