Antonio García Martínez, writing for Vanity Fair:
Google Plus was Google finally taking note of Facebook and confronting the company head-on, rather than via cloak-and-dagger recruitment shenanigans and catty disses at tech conferences. It hit Facebook like a bomb. Zuck took it as an existential threat comparable to the Soviets’ placing nukes in Cuba in 1962. Google Plus was the great enemy’s sally into our own hemisphere, and it gripped Zuck like nothing else. He declared “Lockdown,” the first and only one during my time there. As was duly explained to the more recent employees, Lockdown was a state of war that dated to Facebook’s earliest days, when no one could leave the building while the company confronted some threat, either competitive or technical.