The US military has revealed one of its unclassified US military network was breached earlier this year by Russian hackers who had access to the network for hours before they were discovered. Defense Secretary Ash Carter said their systems detected the breach after the Russian hackers gained access to the network via an old vulnerability which was left unpatched. Carter used the incident to show the growing cyber threat and the need to improve the military's ability to respond. The secretary warned that the United States is ready to help defend US networks and is willing to use cyber weaponry, saying that "adversaries should know that our preference for deterrence and our defensive posture don't diminish our willingness to use cyber options if necessary."

The hackers were quickly discovered within 24 hours by the systems guarding the network which alerted investigators. Carter said the hackers' network activity was then analyzed which pointed to Russia, before the hackers were kicked out "in a way that minimized their chances of returning." Carter did not reveal what the hackers took or what they were after, but said the Russians "are stealthy in their cyber tradecraft and their intentions are sometimes difficult to discern."