From MediaWiki Widgets
This widget allows you to embed any web page on your wiki page using an iframe tag.
Created by Sergey Chernyshev
Using this widget
For information on how to use this widget, see widget description page on MediaWikiWidgets.org.
This widget shouldn't be used on a publicly-editable wiki.
While the url is validated to be a valid url, there is no way the widget can check the contents of the page that is included. When enabling this widget, you allow any user that can edit to include any page, including malicious pages (containing trojans, backdoors, viruses etc), pages that brake out of the iframe and pages that look like your site, but actually is a copy used for phishing.