Early one morning in April last year, someone accessed an underground vault just south of San Jose, California, and cut through fiber-optic cables there. The incident blacked out phone, Internet and 911 service for thousands of people in Silicon Valley.

Such incidents, often caused by vandals, seem fairly common, but exactly how often do they occur? Since 2007, the U.S. telecom infrastructure has been targeted by more than a thousand malicious acts that resulted in severe outages, according to data obtained by IDG from the Federal Communications Commission (FCC) under the Freedom of Information Act.

The FCC requires carriers to submit reports when an outage affects at least 900,000 minutes of user calls, or when it impacts 911 service, major military installations, key government facilities, nuclear power plants or major airports.

The reports themselves are confidential for national security and commercial reasons, but aggregate data provided by the FCC shows there were 1,248 incidents resulting in major outages over the last seven years.

While the data shows no clear overall trend, the years with the highest number of incidents were recent—222 outages reported in both 2011 and 2013.

Cable thieves and gun shots

For the last three years, vandalism was the single biggest cause of outages identified, accounting for just over a third of the incidents in each year.

Gun shots accounted for 9 percent of the outages in 2013, 7 percent in 2012 and 4 percent in 2011. Cable theft accounted for roughly similar levels—4 percent of outages in 2013, 8 percent in 2012 and 7 percent in 2011. The FCC didn’t list all the causes.

Two of the outages over the seven-year period were related to terrorism. Both came as a result of the Boston marathon bombing in April 2013 and apparently refer to widespread cellular outages in the hours after the attacks.

The FCC didn’t respond to several requests for comment on the data. Telecom carriers and their industry association also didn’t respond or declined to comment, citing the sensitivity of the subject.

Telecom isn’t the only infrastructure area to be targeted. Indeed, minutes after the fiber cables were cut in San Jose last year, snipers opened fire on a nearby electrical substation in an attack some believe was terrorist-related.

Most of the incidents in the FCC’s telecom data likely have more mundane causes, such as copper cable theft, a problem carriers have discussed in the past. In 2013, Verizon twice offered rewards of $50,000 for information leading to the arrest of cable thieves who caused numerous outages in the Pittsburgh area. Carriers have been pushing state legislators to make cable theft a federal crime.

Details of each incident in the FCC’s data are hard to come by, and media reports are often the best way to track them. For example, a recent outage hit Time Warner Cable in California’s Riverside county and was blamed on the theft of fiber optics from a telephone pole.

Writing on a company blog in 2011, Level 3 Communications said about 7 percent of its annual outages were due to “people using our fiber cable for gun practice.”