Captcha removed from the plugin. Instead security check has been added in Tell A Friend form submit page. With this new option Tell A Friend form accept submission only from your website domain. It simply reject the submission other then your website domain. After plugin upgrade, Please deactivate and activate the plugin once.

git-svn-id: https://plugins.svn.wordpress.org/wp-tell-a-friend-popup-form/trunk@938536 b8457f37-d9ea-0310-8a92-e5e31aec5664