Mother Jones magazine has revealed a private security firm staffed by former Secret Service agents spied on several environmental groups beginning in the late 1990s. The firm, Beckett Brown International, later S2i, stole documents from trash bins, planted undercover operatives within groups such as Greenpeace, collected phone records and spied on meetings. The company has worked for clients including the Carlyle Group, Wal-Mart, Monsanto and Halliburton.