BRUSSELS — A quarter of a century after the Al-Qaeda attacks on the United States, jihadist groups still pose a major threat to security in Europe, but a new menace has surfaced that is driven mostly by young people online and the authorities are worried.

The exact size of the network behind what is being called nihilistic violent extremism is unclear. But police investigators from nine European countries found about 4,340 URL web addresses linked to “The COM,” as the online community has become known, during a campaign to disrupt it in June and July.

“It’s violence for the sake of violence,” European Union Counter-Terrorism Coordinator Bartjan Wegter told The Associated Press in an interview, ahead of the 25th anniversary of the Sept. 11 attacks on New York and Washington in 2001.

Overall last year, 45 terrorist attacks were reported across 10 of the 27 EU countries, although none of them were major, mass-casualty incidents. About half were foiled or failed, but six people were killed. A total of 486 people suspected of terror links were arrested in 21 member countries, according to the EU police agency Europol.

Jihadist groups — often guided or inspired by networks outside Europe — were behind 24 of the attacks and accounted for more than 70% of the arrests.

Of all those taken into custody, around one third were aged under 18, mostly boys.

Europol does not keep statistics on nihilistic violent extremism because definitions of it differ and acts can fall into the category of ordinary criminality as well as terrorism.

But in Finland in 2025, a 16-year-old boy stabbed three female student colleagues. He allegedly shared a “manifesto” in WhatsApp groups, recorded the attack on Snapchat, and asked on social media for someone to save and give him the video after his release.

In the “manifesto,” he said that he wanted to do something “significant” and “exciting.” No political motive was given for his rampage, according to an EU document on the emerging threat of nihilistic extremist violence.

“It’s very much a fascination with violence. It’s violence as a means of asserting oneself, as a means of gaining status in those online communities,” Wegter told AP. “There’s not a direct link with ideology.”

In Italy last year, a 15-year-old boy planned a murder to gain notoriety online, authorities there said. He kept images and videos of assaults, murders, school shootings and child pornography on his smartphone.

Wegter said these kinds of incidents, which have been on the rise for two to three years, are not isolated but organized by online networks that are “often driven by young people, for young people often involving young boys.”

He said that they “lead to offline violence. We’ve seen stabbings, a young individual stabbing an elderly person for no reason whatsoever.”

Such attacks are tough to prevent or track. They often involve “young individuals who will not have a criminal record, usually, who don’t leave any footprints other than online perhaps, but then it’s often behind encrypted walls and communities,” Wegter said.

High on the list of groups authorities’ radar is 764, which was founded by an American high school dropout, Bradley Cadenhead. He’s serving an 80-year prison sentence for child pornography and sex offenses, but the group still functions.

In Germany last year, a 20-year-old man believed to be a leading 764 member faced 123 charges over acts of “an unimaginable level of brutality and inhumanity,” including murder, rape and the sexual abuse of children, the EU document said.

Unlike 25 years ago — when extremists, mostly from Saudi Arabia, entered the United States and trained to become deadly pilots — the terror threat facing Europe today is mostly organized online.

“The online environment, for all the good things it brings, it is still too permissive,” Wegter said. He described it as “a petri dish for the connection between different threats.”

Privacy advocates insist that people have a fundamental right to communicate without unjustified intrusion. They accuse the authorities and some companies of undermining protections through spyware and other methods.

But Wegter said that “our law enforcement must be equipped with the instruments and tools to deal with the threat as it exists today.” He noted that 85% of investigations take place in the digital environment. “It means that we have to adjust ourselves to that.”

For the Dutch diplomat himself, it means talking more to authorities and organizations in other countries, notably those that such groups use as a rear base. “Because what happens outside our borders impacts on our security,” including what’s being amplified online, he said.

Europol said criminals are exploiting images and audio to create and edit propaganda, including through deepfakes, memes and GIFs. AI-powered bots were also used to boost recruitment and promote terrorist ideologies, while AI-driven app were used for research to prepare attacks.

“The kind of violent content, violence inciting content, propaganda, manuals, tactics, everything that is available, is very much amplified by AI,” Wegter said.