The cuts, in San Carlos and San Jose, California, also disrupted wired and wireless telecommunications services for thousands of users in the region. AT&T, which owns the main affected fibers, expected service to be restored by Thursday evening. Police suspect vandals did the damage, which would have involved removing manhole covers and using cutting tools to sever thick cables that each contain many strands of fiber. AT&T, Verizon and Sprint Nextel users were affected.

The main cut took place in the southern part of San Jose, just a few miles from the IBM Silicon Valley Lab, a research center for cloud computing and other technologies. That lab was effectively shut down by the outage, as was an IBM manufacturing facility on Hellyer Avenue, near the site of the cut. Apart from small maintenance crews, employees were told to work from home, IBM spokeswoman Jenny Hunter said. Though IBM demonstrates some of its cloud systems at the Silicon Valley Lab, it doesn't host public cloud services there.

In addition, at least one server was affected at the Internet Assigned Numbers Authority (IANA), which translates between domain names and Internet addresses. The outage cut off one of IANA's public test systems for DNSSEC (Domain Name System Security Extensions), an emerging protocol designed for more secure domain-name lookup, according to an official notice on a DNSSEC mailing list.

But the cuts did not seem to affect the technology giants of Silicon Valley, whose lifeblood is high-speed Internet access, mostly delivered over such fibers. Google, Yahoo and Cisco Systems said their operations were not affected.

In San Jose, vandals apparently entered a manhole between a highway and a railroad track at about 1:30 a.m. and cut four AT&T cables. In San Carlos, about 40 miles north of the San Jose site, some AT&T cables as well as some Sprint cables were cut underground. That attack apparently happened between about 4 a.m. and 5 a.m., said San Carlos Police Department spokesman Rich Cinfio. The San Jose incident affected people in a small area of the city of San Jose, as well as in Santa Cruz and San Benito counties to the south, according to San Jose Police Department spokesman Sgt. Ronnie Lopez. Because emergency 911 calling service was disrupted, law enforcement deployed more officers in some areas to make them more accessible, he said.