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Bessen & Meurer (2012) estimate that non-practicing entities have accrued $29 million of direct costs to businesses during 2011.[http://papers.ssrn.com/sol3/papers.cfm?abstract_id=2091210##] The two Boston University faculty members have also published a book, ''Patent Failure: How Judges, Bureaucrats, and Lawyers Put Innovators at Risk'' [http://www.amazon.com/Patent-Failure-Bureaucrats-Lawyers-Innovators/dp/069113491X/arstech-20], where they claim patent trolls "cost publicly traded defendants $500 billion since 1990."[http://arstechnica.com/tech-policy/2011/09/study-patent-trolls-have-cost-innovators-half-a-trillion-bucks/]