As football fans count down to Super Bowl 50, federal authorities, including the FBI and Department of Homeland Security, are looking into security concerns at Levi's Stadium in Santa Clara, California, NBC News reported Sunday. Officials investigated a series of incidents where fiber optic cables had been severed in California, treating them as a possible security risk for the Feb. 7 NFL championship game.

"Particularly with the rise in use by terrorist groups of the internet to inspire and recruit, we are concerned about the 'self-radicalized' actor(s) who could strike with little or no notice," homeland security officials said in a report, as quoted by NBC news. Fiber optic cables have been repeatedly severed throughout California since the summer of 2015, stumping FBI investigators as to who is cutting them and why. Severed cables slow down internet service, financial transactions and even emergency calls and are treated as a potential preparation for terrorism, the Wall Street Journal reported in August 2015.

The threat of lone wolf terrorism has increased after a self-radicalized couple stormed an office Christmas party in San Bernardino, California, in December, opening fire on employees in an act that killed 14 and wounded many more. Authorities have not been able to connect the pair to any formal training in Syria with the Islamic State group or any other terror group, leading many investigators to believe the attack was a case of homegrown terrorism.

Terrorists who pledged allegiance to ISIS descended upon Paris two weeks before the San Bernardino massacre, slaughtering 130 people in locations across the city, at targets including a large stadium. The assault was the worst massacre on French soil since World War II, and it sparked fear in city residents around the world as it targeted cafes, bars and other nighttime gathering spots.

The FBI noted how among the Paris attacks was an attempt to bomb a big stadium, the Stade de France. The report said one potential security risk would be bars, parking lots or anywhere else fans congregate outside the Super Bowl stadium because they could not be as easily protected by police.