Two more fiber optic cable lines were severed in California, bringing the number of attacks on data lines in California since July 2014 to 16, the FBI said on Wednesday.

The FBI is investigating what AT&T said were fiber cuts at two different manholes in Livermore, just southeast of San Francisco late Monday. Internet service in the region was curtailed until crews repaired the damage Wednesday morning.

"It's something the FBI is taking very seriously," bureau spokeswoman Michele Ernst told Ars in a telephone interview.

AT&T said it is offering a $250,000 reward to capture whoever is responsible for sabotaging a part of the area's Internet infrastructure.

The authorities suspect that the vandals, who operate at night, may be posing as telecom workers. All the while, the sabotage continues unabated.

The affected lines are about as thick as a finger and are covered with flexible conduit. They often carry Internet, television and phone calls. The cuts have been performed in areas where there are no security cameras.