South Korea's financial watchdog is probing a major local construction firm over whether it has intentionally hidden applicable risk factors in selling bonds to investors while being fully aware of such risks, informed sources said Thursday. According to the sources, the Financial Supervisory Service (FSS) is looking into GS Engineering & Construction Co.'s sale of corporate bonds totaling 380 billion won (US$356 million) in February of last year, which came just two months ahead of its announcement of its first-quarter earnings.