In 2009, someone broke into the Climatic Research Unit of the University of East Anglia in the UK and stole emails. The material was distributed online - mainly on blogs linked to climate change sceptics. It was used to make the case that scientists were surreptitiously twisting the facts to exaggerate climate change. That was not the case. But before that became clear, events would take on a life of their own, sparking a global media storm. BBC Security correspondent Gordon Corera goes on the trail of this ‘cyber cold case’ to try and discover who was behind ‘Climategate’.