Synack Inc., a startup founded by two former NSA staff, has raised $7.5 million in financing from investors led by Kleiner Perkins Caufield & Byers. The Menlo Park company has developed a business model where it offers financial incentives for security specialists—or "white-hat hackers"—to find security holes in networks and systems. Also joining in the Series A round were Google Ventures, Allegis Capital, and Derek Smith, the CEO of Kleiner Perkins-backed Shape Security. Synack was founded…