PITTSBURGH (AP) - The U.S. Department of Justice's top national security prosecutor on Wednesday called for increased vigilance by people to combat the home-grown terrorists being created over the Internet by the Islamic State group.

Assistant Attorney General for National Security John P. Carlin said the threat from the Islamic State is different from that posed by al-Qaeda and other more structured groups because the Islamic State uses the Internet to target and radicalize people and encourage them to commit attacks where they live.

"What they've essentially done is franchise out terrorism," he said.

Carlin spoke with reporters before a speech he was to give to the National Cyber-Forensics & Training Alliance in Pittsburgh.

The public-private nonprofit aims to defeat cybercriminals by helping businesses and government investigators share intelligence about cyberattacks. It works in conjunction with an FBI cybercriminal squad based at the agency's Pittsburgh field office.

While home-grown terrorists are less likely to pull off "large-scale, spectacular attacks" like the Sept. 11 hijackings, Carlin said, the threat such lone wolves pose can be more difficult to track because even people close to them may not know they're terrorists or wannabes.

Carlin said the FBI is investigating such efforts in all 50 states but because the Islamic State can reach people through their home computers those communications are difficult to track.

"So much of the critical infrastructure is in private hands," he said.

Carlin said parents or others who see suspicious behavior should report it, even if it results in prosecution of a loved one.

"What person would want their child or parent or loved one to kill other innocent people inside the U.S.?" he said.

The Islamic State group targets younger people with confusing images meant to soften its violent stance, such as a person holding a kitten in one hand and a gun in the other, Carlin said.

The group monitors the Web responses of such young people and, once it's convinced they're ready to commit terrorist acts, will communicate with them using encrypted sites. Those messages can sometimes include detailed instructions on how to carry out a bombing or other kind of attack.

Carlin also addressed efforts by the Department of Justice and Pittsburgh-based U.S. Attorney David Hickton to combat other cybercrimes. He mentioned the indictments of five Chinese People's Liberation Army officers by Hickton in 2014 on charges they stole trade secrets from Westinghouse, U.S. Steel, Alcoa and specialty steelmaker Allegheny Technologies Inc.

Though it's unclear whether those officers will be prosecuted, Carlin said the Chinese are getting the message. He noted that Chinese President Xi Jinping recently acknowledged that such activity is theft.