© Danny Moloshok / Reuters

FBI agents in California are investigating the cutting of two AT&T fiber optic cables earlier this week - at least the 11th such attack in a year. The telecommunications company is offering a $250,000 reward for information.The most recent attack - which took place in the town of Livermore, a San Francisco Bay Area suburb - involved the cutting of cables in two different manholes at about 10:30 p.m. local time on Monday, AT&T said in a statement.The thin cables carry vast amounts of data, including phone calls, computer transactions and emails."It's being taken very seriously by the FBI and our law enforcement partners," said Michele Ernst, a spokeswoman for the bureau's San Francisco field office.It comes just two months after someone severed at least three fiber optic cables in an underground vault in Alameda County, California, which disrupted internet and phone service around Sacramento for 20 hours.Meanwhile, security experts believe the attacks may be the work of a disgruntled employee, or of terrorists aiming to determine how long it takes to repair the infrastructure.