Activist investor Starboard Value upped the pressure on Yahoo CEO Marissa Mayer, demanding the company shake up management and calling for a spinoff or sale of the company’s core search and advertising business. The management team led by Mayer has “failed to produce acceptable results, in turn, causing massive declines in profitability and cash flow,” Starboard Managing Member Jeffrey Smith wrote in a letter to Yahoo’s board on Wednesday. Read the original story from the New York Post.