Symantec Corp., the computer-security company synonymous with "antivirus," fired Chief Executive Steve Bennett amid sagging revenue and slumping shares, the second time it has dumped a CEO in less than two years.

Mr. Bennett had been CEO since July 2012, when he replaced Enrique Salem. A former General Electric Co. executive and Intuit Inc. chief executive, Mr. Bennett had initially joined Symantec as chairman. He aimed to retool Symantec to compete with a new generation of cybersecurity companies.

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