Antivirus and security software provider Symantec Corp fired Chief Executive Steve Bennett on Thursday, the second time it has sacked its top executive in less than two years, as the company struggles to revive growth amid eroding PC sales. Shares of the company, known for its Norton antivirus software, fell 10 percent in extended trading. Symantec said it appointed board member Michael Brown as interim president and CEO. The decision to let go of Bennett was “the result of an ongoing deliberative process and not precipitated by any event or impropriety,” the company said.