German Justice Minister Katarina Barley has spoke to Facebook executives to find out whether the country's 30 million users were affected in the mishandling of personal data. A whistle-blower earlier revealed that a London-based consultancy improperly accessed user information from Facebook to build profiles on US voters. The information was later used to help elect US President Donald Trump in 2016. Barley said it must be made possible for users of social media sites to specify whether they are happy for their data to be used in certain ways, rather than just giving them the option to tick "yes", or not be able to use the service.