U.N.I.T. (tie-in website)

U.N.I.T. was a website launched on 18 April 2005 to coincide with the 2005 series of Doctor Who, specifically World War Three, one of several websites created at that time. On 20 April, the Doctor Who website added a link to the U.N.I.T. website, visible as "Alien Hotline", after the site updated to focus on World War Three.

Everything on the website was told from an in-universe perspective, as if you were reading the very pages on the in-universe website itself. The website prominently featured many references to the original and early revival eras of Doctor Who.

The United Nations' Legal Actions
It was because of this website using the original UNIT acronym (United Nations Intelligence Taskforce), the real world United Nations took legal action against the BBC and the acronym was hastily changed to the Unified Intelligence Taskforce.