A Facebook funeral party at its HQ once descended into violence - and security suspected gang involvement

Steve Jennings/Getty Images for Little Kids Rock

Bands performing at a party on Facebook's Menlo Park, California campus in 2015. (This is not the party described in this story.)

• Facebook has a 6,000-person security army guarding its employees around the world.
• But they don't just safeguard against outside threats - they also sometimes have to protect workers from each other.
• Business Insider has published a 5,000-word investigation into Facebook's Global Security team.
• In one incident in 2013, a memorial party for a beloved employee descended into apparently gang-related violence.

In July 2013, Facebook's beloved head chef Josef Desimone died in a tragic motorcycle accident.

To commemorate him, the company threw a blow-out party on campus at its Silicon Valley headquarters one Saturday the following month. Hundreds of people were invited, and booze flowed freely as Facebook's employees and contract workers gathered to celebrate his life.

And then it descended into chaos.

Multiple fights broke out among attendees, which security staff believe were gang-related, sources said. The event culminated in one kitchen worker being beaten so badly by another attendee on Facebook grounds that they were hospitalised.

The assailant was banned from Facebook's campus, but he continued to sneak back - to visit his mother who worked there.

The incident highlights the challenges Facebook's security team faces as it polices the Silicon Valley technology firm - not only to defend the company from outside threats, but also, sometimes, to protect workers from each other. Business Insider has spoken to 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.

Sources described a hidden world of stalkers, stolen prototypes, state-sponsored espionage concerns, secret armed guards, car bomb concerns, and more. Today, there are a staggering 6,000 people in Facebook's Global Security organisation, working to safeguard Facebook's 80,000-strong workforce of employees and contractors around the world.

When numerous employees' headphones were disappearing a couple of years ago, the company installed a covert mobile camera to monitor desks, a source said. (The sting operation caught an employee stealing them to sell online. A Facebook spokesperson said items are sometimes misplaced during office moves, and then misreported as thefts.)

But Silicon Valley's tradition of openness can complicate things, such as the time when an old prototype of an Oculus virtual-reality headset was stolen from a conference room. Facebook - like many companies - doesn't have surveillance cameras inside its offices, and the enormous open-plan design of the office meant that the pool of suspects would likely be hundreds of people, with no way to narrow it down. There was nothing security could do; the prototype was never recovered.

"The business has identified that we really need that open office environment that promotes our collaboration, and so that's the risk we're willing to accept inside an office is that open office environment," Facebook corporate security chief Nick Lovrien said about Facebook's approach to openness. "So what we then look at is how we mitigate that risk," from proactively sifting through intelligence to putting physical checkpoints in place and manning the perimeter of the offices.

At least one employee has been caught letting in tourists who wanted to take unauthorized tours of the facilities, and employees are also caught having sex in the office about every three months, on average. (Human resources may be alerted, but the couple isn't typically fired.)

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