With sincere thanks to the associated URL, this is .htaccess code that can be used with b2evolution to deny access to requestors who include http: or ftp: on the query string. This is slightly different than the other post - it seems to be working. [L,F] didn’t work as I would have liked.

.htaccess

RewriteEngine On
RewriteCond %{QUERY_STRING} ^.*=(ht|f)tp\://.*$ [NC]
RewriteRule ^.*$  403.php [L]


# CATCH EVERYTHING INTO B2EVO:
# The following will allow you to have URL right off the site root,
# using index.php as a stub but not showing it.
# This will add support for URLs like:  http://example.com/2006/08/29/post-title
# Redirect anything that's not an existing directory or file to index.php
#
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^.*$ index.php [L]

403.php

header('HTTP/1.1 403 Forbidden');

I hope this is helpful.