Officials say the terrorism landscape has changed after the recent shooting in California and Tuesday's threats made to New York City and Los Angeles public schools.

Speaking at the NYPD Shield Conference Wednesday, FBI Director James Comey said that over the last two years, there has been a major "paradigm shift" in how terrorists threaten the safety of the public.

Officials said one of the biggest weapons in the arsenal of attackers is the high-tech encryption present in the web and smartphone applications.

"The use of encryption is at the center of terrorist tradecraft for the last two years," Comey said. "Post Snowden, they made a move. They change the way they conduct themselves to thwart our ability to see them."

NYPD commissioner Bill Bratton said police will be working with law enforcement partners in the United States and around the world to combat terrorism.