Facebook has armed guards covertly patrolling its idyllic Silicon Valley headquarters

Elise Amendola/AP Images

The interior of one of Facebook's offices.

• Facebook has a 6,000-person security army guarding its employees around the world.
• This includes plain-clothes off-duty police officers that covertly patrol its offices with concealed firearms - though most employees don't know they exist.
• Business Insider has published a 5,000-word investigation into Facebook's global security team.

After a disgruntled YouTube user shot three people at the company's headquarters in Silicon Valley in April 2018, Facebook sprang into action.

The social networking firm's offices are just a 30-minute drive away from YouTube, and it swiftly redoubled its own defenses - spooking some employees in the process.

Though most workers don't realise it, Facebook quietly has off-duty police officers in civilian clothes covertly patrolling its headquarters with concealed firearms in case of emergencies. Following the YouTube shooting, Facebook upped their numbers, in doing so unsettling some employees who subsequently noticed them.

Business Insider has spoken with current and former employees and reviewed internal documents for an in-depth investigation into how Facebook handles its corporate security, which you can read in full here.

The incident highlights the challenges Facebook's security team faces as it polices the Silicon Valley technology giant, and the extreme threats it needs to plan for while maintaining a comfortable atmosphere at Facebook's famously luxurious Menlo Park, California headquarters.

In an interview, Facebook's chief global security officer Nick Lovrien said that the company immediately increased its "security posture" following the YouTube shooting. "Not everybody was aware that we had those on campus, so there was a population that was concerned that we had armed off-duty officers," he said.

"But I will say that the majority of people expressed they were much more comfortable having them, and in this role my job is really to weigh that risk versus anything else, and safety is the number one priority, and this was the right investment to be able to mitigate that."

All told, there are now more than 6,000 people working in Facebook's Global Security team - including legions of security officers. CEO Mark Zuckerberg also has armed guards outside of his Bay Area residences, and executive protection officers in civilian clothes quietly keep watch over him while he works in the office and accompany him wherever he goes.

Forewarned is forearmed

Global Security has extensive plans and best practices for a broad array of security incidents, Business Insider learned as part of its investigation into Facebook's security practices.

Executive kidnapped? Notify law enforcement, get proof of life, contact the kidnap-and-ransom-insurance company, and go from there. Active shooter? Gather critical information about the location and description of the shooter, call law enforcement, send out emergency notifications, lock down or evacuate the buildings as necessary, and so on.

Unexpected package sent to an executive's home? Get information about who dropped it off, make an incident alert, and send the package to the GSII without opening it. Media turned up outside Zuckerberg's residence? Figure out who they are, why they're there, send a mobile unit to meet them, and notify police if requested by management or the executive protection team.

Protocols like these are by no means unique to Facebook; they provide a clear agreed-upon framework to follow in times of crisis. But they're indicative of the disparate challenges Facebook now faces in protecting its global workforce, from civil disturbances to safely handling the firing of "high-risk employees."

Facebook has to similarly prepare whenever it constructs a new facility: When it built its new Frank Gehry-designed headquarters in Menlo Park, the security threats it was forced to consider involved everything from the risk of earthquakes to the possibility of a plane from San Francisco International Airport falling out of the sky onto the campus, which would cause carnage.

Read Business Insider's full investigation into Facebook's corporate security »