Updated 11:27 a.m. with more details on the nature of the threat.
Police sealed off access to Facebook’s California headquarters for close to two hours on Tuesday evening to investigate the first significant “threat” against the company.
An unidentified caller phoned in an “unsubstantiated threat” to the San Francisco Police Department against Facebook’s Menlo Park, Calif., campus on Tuesday afternoon, Dave Bertini, commander of the Menlo Park Police Department, said in a prepared statement. The exact nature of the threat was not made clear by the department.
However, two separate sources inside of Facebook confirmed to Re/code that the police were investigating a possible bomb threat on the company’s headquarters. Emails and messages between employees inside the Menlo Park headquarters on Tuesday evening were frantic as company security and the police department investigated the situation.
The threat was deemed “not credible” and the police began to clear the scene at 8:30 pm PT.
The threat comes amid escalating tension between tech companies and some Bay Area residents in recent months, underscoring the growing resentment over the gentrification of San Francisco that has made the region prohibitively expensive to inhabit for longtime dwellers.
It is also particularly noteworthy, as it is the first significant scare for the world’s largest social network, which is situated in the relatively sleepy Silicon Valley.
Last week, the city of Menlo Park introduced its first police officer funded not by state tax dollars, but by money donated from a private company — Facebook itself. The “Facebook Cop,” Mary Ferguson-Dixon, will be stationed down the road from the social network’s headquarters. Ferguson-Dixon will work mostly around local schools, but also “to create safety plans for large campuses” like Facebook’s.
This article originally appeared on Recode.net.