A near century-old statute that gives New York state prosecutors unusually broad authority to prosecute securities fraud could prove a powerful weapon as Attorney General Eric Schneiderman probes Exxon Mobil Corp (XOM.N) over whether the oil firm mislead the public and shareholders about the perils of climate change. The 1921 Martin Act, a wide-reaching state law, was dusted off in the early 2000s by former New York Attorney General Eliot Spitzer who used it to aggressively go after Wall Street firms.