MOUNTAIN VIEW — Less than two years after taking over the helm of troubled Symantec, the world’s biggest security software company, CEO Steve Bennett was fired on Thursday in a move that stunned analysts and sent Symantec’s shares tumbling in after-hours trading.

The Mountain View company named board member Michael Brown to take over as interim CEO until a permanent replacement is found.

No reason was given for the termination of Bennett, who was hired to replace ousted CEO Enrique Salem in July 2012, in hopes of reviving the struggling company. Because Bennett, previously Intuit’s CEO, was widely regarded as moving the company in the right direction, his firing left some industry experts flabbergasted.

“It’s a shocker,” said FBR Capital Markets analyst Daniel Ives. “This is a major, surprising move that they are getting rid of their CEO just as its recovery is playing out. They’re off to a very positive start. It’s a head-scratcher at this juncture. With him not there, you could see a lot of investors start to throw in the towel.”

Before the announcement, Symantec’s shares rose 33 cents to $20.91 at the market’s official close. But after the company reported Bennett’s ouster, its stock price fell $1.56, more than 7 percent, in after-hours trading.

Matthew Casey, an analyst with Technology Business Research, also expressed surprise.

“It kind of caught me off guard,” he said. “I know the results of their recent quarters haven’t necessarily been the most flashy in terms of growth.” But he added that the changes Bennett was trying to bring about, which largely involved streamlining Symantec’s business, “were the correct changes that needed to be made.”

Best known for its popular Norton antivirus software, Symantec has struggled in recent years against a proliferation of other security companies, such as Palo Alto Networks and FireEye. Its $10.2 billion purchase of Veritas Software in 2005, in an effort to expand into the data storage business, also was widely criticized as a mistake.

In recent years, Symantec’s sales have been flat.

Last summer, Bennett cut about 1,000 jobs from Symantec’s workforce of about 20,000 and tried to find new product niches because slumping demand for personal computers had hurt its anti-virus sales. In recent months, it also has seen its chief technology offer and chief financial offer leave. But Symantec officials were vague about why Bennett was fired.

“We recognize Steve’s contributions to Symantec, including developing and leading a series of successful initiatives focused on organizational realignment, cost reduction and process effectiveness,” the company said in a statement. “These changes have helped establish a solid foundation for Symantec’s future.”

The statement added that “our priority is now to identify a leader who can leverage our company’s assets and leadership team to drive the next stage of Symantec’s product innovation and growth. This considered decision was the result of an ongoing deliberative process, and not precipitated by any event or impropriety.”

But that explanation failed to satisfy Rick Holland, a principal analyst at Forrester Research.

“This completely caught me by surprise,” he said. “I wonder what happened, for real. What’s the story that we’re not getting here?”

Contact Steve Johnson at sjohnson@mercurynews.com or 408-920-5043. Follow him at Twitter.com/steveatmercnews.