This morning it seems that the Google search engine is reporting popular websites as being harmful. After searching for information on "dogs" this morning Google reported the Wikipedia article as being harmful. A search for "joomla" showed the same messages for all the search results. See the screenshots below. In fact other searches produced the same result, a "This site may harm your computer." message.

Google Search for Dogs reports a wikipedia article as harmful.

According to Google the Joomla.org website is harmful.

Update: It seems that Google has fixed to problem.