The CFO of FireEye, once a Wall Street darling, is leaving and the stock is tumbling

Computer security company FireEye had some good news and bad news for investors.

The bad news: its CFO Michael Sheridan is leaving. He joined in 2011 and is leaving to take a position with a private company, the company said.

The good? FireEye turned in better-than-expected second quarter results and upped its guidance for next quarter.

Investors were not pleased. The stock went tumbling in after-hours trading and is down almost 7%.

Specifically, FireEye generated revenue of $147 million in the second quarter versus the $143 million expected by analysts. The company posted a loss of 41 cents per share, excluding certain items, compared to the 48 cents per share loss that Wall Street was expecting.

But the CFO change is worrisome for investors.

FireEye was once a high-flying stock at the start of 2014. The company had a spectacular, oversubscribed IPO in the fall of 2013, in which it raised more than $300 million. Wall Street analysts loved its technology, which protects companies from the hardest-to-protect-against hacker attacks.

The stock soared to a high of more than $97, turning its founder, momentarily, into a billionaire. So the company turned around and sold another 5.6 million shares and raised another $300 million.

But it's been burning through the cash. A few months ago, the company did a convertible debt offering of $800 million, upping the offering by $200 million.

In June, Barclays and USB downgraded the stock (though, Oppenheimer was bullish and upgraded it).

From a high of $95 in 2014, the stock has been on roller coaster. It's currently trading at about half that price.

While the company isn't projecting profits anytime soon, it is growing really fast. Second quarter billings were $178.3 million, up 57% from the year-ago quarter.

FireEye now expects to post a loss of 44 cents to 48 cents per share during the third quarter, versus the average analyst consensus of a loss of 46 cents per share. FireEye sees Q3 2015 revenue of $225-230 million, versus the consensus of $164.3 million.