With one of the fastest-rising head counts in Silicon Valley, security darling FireEye has announced a $457 million (£280 million) secondary offering to raise cash for even more hiring and future acquisitions.

This being a boom time for the firm’s shares and security in general, the financial engineering is slightly complicated. The 14 million shares on offer will include 5,582,215 from FireEye, with the remaining coming from stock holders; the firm will only benefit from the shares it issues, equivalent to $457 million out of a total of around $1.1 billion.

What is all this new money actually for?

"We expect FireEye to invest in head count expansion, M&A, and capital expenditures that will position the company for strong continued growth over the coming years, which could prove our estimates to be conservative," FBR Capital Markets’ Daniel Ives told Reuters.

Early in 2014, FireEye used up some of its IPO war chest buying another touted security firm in the anti-APT space, Mandiant, for $1 billion. Mandiant’s founder and FireEye COO, Kevin Mandia, then turned up with a part-time job on the board of phishing training outfit, PhishMe.

Since its IPO in September 2013, FiireEye’s share price has soared to nearly three times the opening price, probably making its founder, CTO and largest shareholder a new Silicon Valley paper billionaire according to Forbes magazine, which obsesses about such details. All this from a firm founded as long ago as 2004.

Before and since its IPO, FireEye has been in a hiring binge not unusual for Silicon Valley software startups but unusual for a security firm. That is why FireEye is being watched by the industry; it seems different but perhaps slightly unstable. Acquisitions could be a good influence.

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