This was done, according to the SMH article, Wikipedia added to child pornography blacklist, due to the identification of a photo in one article (of the more than 2.6 million articles in Wikipedia) as being of a sexual nature and the entire site being added to the child pornography blacklist (ironically the same list that Senator Conroy has discussed using in Australia).
Fortunately this block was dropped very quickly, as reported in PC World, U.K. Wikipedia Blacklisting Dropped.
The image in question, of a 1976 German album cover, has not been banned elsewhere in the world, was publicly available in a physical form (as the cover of an album) and is digitally available at many other websites including Amazon.
Per the PC World article, in a facesaving effort, which ironically emphasises the difficulties of filtering the internet, the Internet Watch Foundation (IWF), the nonprofit group that blacklisted the Web page, stated that,
The image in the Wikipedia article is hosted outside the U.K., an issue addressed by the IWF in its statement Tuesday. "Any further reported instances of this image which are hosted abroad, will not be added to the list. Any further reported instances of this image which are hosted in the U.K. will be assessed in line with IWF procedures."
The IWF lamented that while its goal is to minimize the availability of indecent images of children on the Internet, its decision to blacklist the Wikipedia article "had the opposite effect."