U.S. law enforcement officials are warning members of Congress about the danger of terrorists—and their supporters—using encrypted communication and private messaging.

By so doing, quickly changing technology makes it harder for the government to monitor possible terrorists, the officials told members of the U.S. House Committee on Homeland Security during a June 3 hearing. Groups like ISIS (also known as ISIL) use the Internet and social media to recruit, share their propaganda and to inspire attacks.

Presenting himself before the Committee on Homeland Security of the U.S. House of Representatives on June 3, Michael Steinbach, assistant director at the FBI, said in a statement, “As technology advances so, too, does terrorists' use of technology to communicate—both to inspire and recruit.”