Passwords that took seconds to guess, or were never changed from their factory settings. Cyber vulnerabilities that were known, but never fixed. Those are two common problems plaguing some of the Department of Defense's newest weapons systems, according to the Government Accountability Office. The flaws are highlighted in a new GAO report, which found the Pentagon is "just beginning to grapple" with the scale of vulnerabilities in its weapons systems. Drawing data from cybersecurity tests conducted on Department of Defense weapons systems from 2012 to 2017, the report says that by using "relatively simple tools and techniques, testers were able to take control of systems and largely operate undetected" because of basic security vulnerabilities. The GAO says the problems were widespread: "DOD testers routinely found mission critical cyber vulnerabilities in nearly all weapon systems that were under development." The Pentagon has only recently made it a priority to ensure the cybersecurity of its weapons systems. It's still determining how to achieve that goal - and at this point, the report states, "DOD does not know the full scale of its weapon system vulnerabilities." Part of the reason for the ongoing uncertainty ... is that the Defense Department's hacking and cyber tests have been "limited in scope and sophistication." When problems were identified, they were often left unresolved. The GAO cites a test report in which only one of 20 vulnerabilities that were previously found had been addressed.