Yahoo! Inc. Chief Executive Officer Marissa Mayer hired Ken Goldman to succeed Tim Morse as chief financial officer, making her biggest management change yet after taking the reins of the struggling Web portal.

Goldman was previously chief financial officer at Fortinet Inc., a provider of computer-network security. His appointment is effective Oct. 22, while Morse, who joined in 2009, is leaving later this year, Sunnyvale, California-based Yahoo said in a statement yesterday.

Mayer, who joined in July, is realigning leadership in her drive to reverse three years of declining revenue and market share losses to Facebook Inc. and her former employer, Google Inc. She may seek to impose fiscal discipline by hiring Goldman, who has helped cut costs and improve oversight at Silicon Valley companies over the past three decades, said Erik Suppiger, an analyst at JMP Securities LLC in San Francisco.