Synack Inc., a security startup supported by a network of white-hat hackers, announced today that it has raised $21.25 million in a Series C funding round led by Microsoft Ventures.

The round also included participation by Hewlett Packard Enterprise Co. and Singtel Innov8, along with existing investors GGV Capital, Google Ventures and Kleiner Perkins Caufield & Byers. The company’s total funding to date is now $55 million.

Founded in 2013 by former National Security Agency security experts, Synack bills itself as a “Hacker-Powered Intelligence Platform.” The company offers a suite of cybersecurity solutions, which are continuously probed and tested by a private crowd of hackers.

Synack’s investors include a number of major enterprise tech companies, which believe that the startup’s hacker model gives it an edge in cybersecurity.

“Traditional security testing presents many challenges that Synack tackles head-on with an innovative, crowd-focused approach,” said Nagraj Kashyap, corporate vice president at Microsoft Ventures.

According to Synack, waiting to react to cyber attacks as they happen is not an effective form of defense, and Chief Executive and co-founder Jay Kaplan said enterprises need to be proactive in tackling potential threats.

“The best defense is a good offense,” Kaplan said in a statement. “Businesses can only stay one step ahead of the adversary by beating them at their own game.”

Synack said it has brought on several Fortune 500 companies, and its year-over-year bookings have jumped 300 percent in the last four quarters. The company will use its new funding to further develop its security platform and scale operations in the U.S. and Europe, and the company plans to expand into the Asia Pacific market. Synack also said that it will “continue to recruit and invest in the most skilled hackers in the world.”

Photo: Synack