The Department of Defense’s attraction to bug bounty programs continues with a contest to find security flaws in its travel booking system.

The Pentagon is again pairing with HackerOne, a private company that has run similar programs for the Air Force, Army and the DoD at large, with hackers reporting hundreds of valid vulnerabilities and the Pentagon paying out hundreds of thousands of dollars.

The latest program is focused on the Defense Travel System (DTS), an enterprise system that DoD personnel use to book things like airline and hotel reservations when they travel for DoD business.

Because DTS is used by millions of people and maintains sensitive information, hardening its security is a priority for DoD, said Reina Staley, the chief of staff for the Defense Digital Service (DDS), which oversees the military’s bug bounty contests under the “Hack the Pentagon” program.

“The quick, positive reception of the [Hack the Pentagon] program has been a major win; inviting hackers to uncover vulnerabilities in DoD assets sounds counterintuitive to traditional government security practice, but the value of crowdsourcing external talent has been clear in every challenge we’ve run to date,” Staley told CyberScoop by email.

The Pentagon is essentially crowdsourcing the security of DTS from a pool of hackers recruited by HackerOne. Participants are probing DTS for vulnerabilities that could be exploited by adversaries. People who submit a valid vulnerability could win money. The program opened April 1 and will close April 29.

“The most security mature organizations look to others for help,” said Alex Rice, HackerOne’s co-founder and CTO, in a press release. “We’re excited to bring a fresh, mission-critical asset to the hacker community with the goal of protecting the sensitive government data it contains.”

Researchers have to apply to participate in the challenge, which is open to 600 participants. HackerOne will choose about 30 percent by lottery and the rest based on the company’s internal reputation system. That means the program is seeking experienced white hat hackers who are familiar with how a bug bounty program works.

HackerOne does not specify on the registration page the bounty ranges or what kind of security vulnerabilities are within the scope of the challenge. Government employees and active duty military personnel can also submit bugs, but can’t win any cash. Participants have to be citizens and residents of the U.S., United Kingdom, Canada, Australia or New Zealand — members of the so-called Five Eyes intelligence alliance.