Twenty years ago, the citizens of communist East Germany were for the first time able to view the files kept on them by the Stasi, the dictatorship's secret police. Today these files fill 100 kilometers of shelves. And there are also around 16,000 sacks of documents that Stasi agents shredded by hand. Scientists from the Fraunhofer Institute in Berlin are now constructing a super-computer that can put the fragments back together. The "snippet machine" is attracting interest from all over the world.