Facebook may have been the target of an attack after a machine at one of the social network's mail-sorting facilities warned of a possible toxic substance.
Menlo Park Fire District said a hazardous materials team is on the scene at the building, which normally has about five or six people working there. Both NBC News Bay Area and KRON 4, which at first said the substance may have been sarin, said no employees were exposed, though initially there were indications two people may have been.
Facebook in a statement said a package delivered to one of its mail rooms was "deemed suspicious" around 11 a.m. PT, without providing additional details.
"We evacuated four buildings and are conducting a thorough investigation in coordination with local authorities," a Facebook spokesman said in a statement, adding that the substance has not yet been identified. "As of now, three of the evacuated buildings have been cleared for repopulation. The safety of our employees is our top priority and we will share additional information when it is available."
The possible attack at Facebook and the response highlight the increasing concerns tech companies and over security, which is spilling over into their home communities.
Last year, a woman shot three people at YouTube's headquarters, about 20 minutes south of San Francisco, before turning the gun on herself. In that case, the shooter appeared to be angry at how YouTube had handled her channels and videos.
Facebook evacuated its headquarters in December of last year, after receiving an anonymous bomb threat that turned out to be a false alarm.
Now, someone's sent a suspicious package to the company too.
Business Insider said an MPFD official said sarin was detected in a mail bag during a routine test, and that its detection may have been a false positive. So far, no one was showing symptoms of exposure.
CBS News confirmed that the Federal Bureau of Investigation is responding to Facebook's headquarters at the request of the hazmat team.
The FBI didn't immediately respond to a request for comment.
This story is developing…
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