Kingsoft Corporation announced two months ago that it would spin off a business unit for Internet security and other services and list its shares in the U.S. Now, the spinoff, Cheetah Mobile, has filed with the U.S. Securities and Exchange Commission for a splashy U.S. IPO Formerly known as “Kingsoft Network” in China, the company developed a web browser called Cheetah. Cheetah Mobile plans to raise $500 million on the New York Stock Exchange.