It is usually acceptable to include links to a website's homepage, unless a statement on the site says otherwise. However, you should not use the website's logos or other branding as linking icons, unless you have explicit permission from the publisher (the person, or body who created the web pages).
Deep linking, linking to parts of a website under or beyond the website's homepage, is generally not allowed by law, particularly where this would bypass branding, sponsorship, legal or policy information. You should not include deep links within Moodle, unless you have explicit permission from the publisher, or a policy statement on the website allows it.
Material on web pages is governed by copyright law. You cannot upload copies of web page material unless you have explicit permission from the publisher (the person, or body who created the material contained on the web pages), or a copyright statement or licence on the web pages specifically permits this.
You can upload text as long as you cite the authors of the article, or provide a direct link back to the article on Wikipedia. This does not include images For full details of permissions see: http://en.wikipedia.org/wiki/Wikipedia:Copyrights
Creators of web page material can use a Creative Commons Licence to specify how their material may be used by other people. A Creative Commons licence icon on a web page indicates that you can use the material without having to seek permission, provided you use it in the manner permitted by the licence. You need to read the licence specific to that website to find out what use is permitted. For full details see: http://creativecommons.org/