US cybersecurity agency warns of ‘grave threat’ after ‘critical infrastructure’ hacked

US authorities have expressed increased alarm about a long-undetected intrusion into computer systems around the world that officials suspect was carried out by Russian hackers.

The nation’s cybersecurity agency has warned of a “grave” risk to government and private networks, after federal agencies and “critical infrastructure” were hacked in a sophisticated attack.

It was hard to detect and will be difficult…