AmiMoJo writes "According to security company Sophos, around 55% of home users and 18% of enterprise users have updated to Mavericks, the latest version of Mac OS (10.9). Unfortunately Apple appears to have stopped providing security updates for older versions. Indeed, they list Mavericks itself as a security update. This means that the majority of users are no longer getting critical security patches. Sophos recommends taking similar precautions to those recommended for people who cannot upgrade from Windows XP."