Deliberate sabotage is being blamed for a sizable internet and telephone service outage Thursday in Silicon Valley.

At 1:30 a.m., someone opened a manhole cover on a railroad right-of-way in San Jose, climbed down and cut four AT&T fiber optic cables. A second AT&T cable, and a Sprint cable, were cut in the same manner two hours later, farther north in San Carlos.

Service for Sprint, Verizon and AT&T customers in the southern San Francisco Bay Area has been lost, according to the San Francisco Chronicle. Police departments have put more units on the street, because nobody can call 9-1-1.

A much smaller Comcast outage affecting around 4,500 customers in San Jose began at around 1:00 p.m. Pacific time. Spokesman Andrew Johnson says the company is investigating the cause.

Update: AT&T is offering a $100,000 reward for information leading to the arrest and conviction of the vandal.

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