Awwal 25, 1432 H/Feb 28, 2011, SPA -- A government agency devoted to uncovering the crimes of East Germany's Stasi secret police said Monday it had unmasked a staffer who had once been a Stasi officer, according to dpa. The Berlin agency, which preserves the Stasi files, has confirmed in the past that its building security unit employs about 50 guards who were similarly employed when the Stasi was operational. But those guards are monitored to make sure they do not damage files. Hundreds of other staff, including historians and librarians, are carefully vetted to prevent former Communists from tampering with the files stored at the agency. The agency's work is highly regarded in Germany for tracking the Stasi's influence on daily East German life, keeping a record of agents and informants and restoring documents destroyed in the waning days of East Germany. Stasi influence was pervasive in East Germany, with many agents supervising thousands of informants, some of whom were coerced into helping the Stasi. Andreas Schulze, an agency spokesman, said the unmasked staffer, who worked in the software department, had been a lieutenant in the Stasi, which was closed down in early 1990 after the Communists fell from power in popular protests and East and West Germany reunited. Schulze said the man had had no ability to erase files, as his job was only to monitor the compatibility of the agency computers with other government computers in Berlin. He was one of tens of thousands of East German officials who kept their jobs after unification. Not all East German officials were necessarily Stasi agents. "Of course the case is a blot, but it belongs in the context of problems that we have inherited," said the spokesman. Another man, who worked at the archives agency for years before being seconded to another department, resigned Friday after being labelled a former Stasi operative.