It even came up during this week's Republican presidential candidate debate. But despite all the attention focused on backdoors lately, no one noticed that someone had quietly installed backdoors three years ago in a core piece of networking equipment used to protect corporate and government systems around the world.

On Thursday, tech giant Juniper Networks revealed in a startling announcement that it had found "unauthorized" code embedded in an operating system running on some of its firewalls.

The code, which appears to have been in multiple versions of the company's ScreenOS software going back to at least August 2012, would have allowed attackers to take complete control of Juniper NetScreen firewalls running the affected software. It also would allow attackers, if they had ample resources and skills, to separately decrypt encrypted traffic running through the Virtual Private Network, or VPN, on the firewalls.