Despite reporting strong second quarter results on Thursday, security firm FireEye saw shares tumble in after-hours trading, on the news that CFO Michael Sheridan has quit the company for a job at "a private technology company in an unrelated industry."

Sheridan, CFO at FireEye since 2011, tendered his resignation on Tuesday, July 28, to take effect Monday, August 3, according to regulatory filings. The short notice of his departure is unusual for the officer of a public company.

FireEye Vice President of Finance Frank Verdecanna will take over as interim CFO while the company searches for a permanent replacement.

The personnel news overshadowed an otherwise strong earnings report, with FireEye reporting record revenue of $147.2 million for a net loss of 41 cents per share. Analysts had expected $143 million in revenue for a per share loss of 41 cents, according to Barron's.

No stranger to the startup world, Sheridan previously served as CFO of a fledgling Facebook in 2006, according to his LinkedIn profile. On a call with investors, Sheridan said his decision to resign was "solely motivated by the alignment of the challenges of this new role with my personal interests," and in no way a reflection of dissatisfaction at FireEye.

FireEye stock was down as much as 5 percent in after-hours trading.