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One booming business in Silicon Valley is security — but not the digital kind.

Insiders tell Page Six that the young tech billionaires are forced to hire armies of guards after threats from unstable users.

Sources told us that Facebook mogul Mark Zuckerberg has 16 bodyguards now working at his home.

“He has guards over at his place,” said a Palo Alto, Calif., insider, adding that tech moguls around town are all quietly upping security.

We hear that Zuckerberg’s 16-person detail are not all on the scene at the same time, but work in shifts.

“You’re touching hundreds of millions of people,” a Silicon Valley source pointed out of the digital landscape, adding that threats from even a tiny percentage of disgruntled users who work the apps for endless hours can be unnerving — “All the CEOs get threats, and they take them very seriously.”

The source noted that threats can disturbingly extend to family members.

Facebook said it had more than a billion “daily active users on average” for December 2015.

Our source also pointed out that Facebook’s become a reported leading reason for romantic breakups and divorces, which can cultivate angry users who would unfairly blame the site.

The American Academy of Matrimonial Lawyers has said, “Facebook holds the distinction of being the unrivaled leader for online divorce evidence.”

Meanwhile, Zuckerberg’s security detail has annoyed locals at his $10 million San Francisco “pied-à-terre.”

Neighbors last month accused his detail of “permanently . . . illegally” taking up two prime parking spots in the area.

A letter posted by residents said, “We’ve spoken to the security guards, and they were cordial but ultimately have been instructed by their supervisors to not move the cars under any circumstances.”

That followed other skirmishes with Zuckerberg’s neighbors over issues including construction.

He also owns a $7 million home in Palo Alto and spent $30 million in 2013 to buy up four neighbors’ homes, then leased them out.

A Facebook rep didn’t comment.