Italian prosecutors say two men behind a Twitter account that carried threats in the name of the Islamic State group were targeting an Italian military base near Brescia that has a U.S. military presence. Head of anti-terrorism unit Lamberto Giannini, left, and Prosecutor Maurizio Romanelli listen to a question during a news conference to illustrate an anti-terrorism operation, at the police headquarters in Milan, Italy, on Wednesday.

WASHINGTON — "He acknowledged the truth, he gives [allegiance], the order has been given, his heart beats, he accepts, butterflies kick in. The target is given, the anticipation is over, a sense of relief."

With this stream-of-consciousness narrative, an Islamic State fighter using the name of Abu Abdullah Britani posted this call May 10 on Twitter to would-be jihadists in the West. Don't second-guess yourself, he cautioned, in messages translated by the SITE Intelligence Group. "Thoughts going through your head, how many will be killed, how will they react, but you snap out. "

This is the menacing but murky face of the "lone wolf" attackers that U.S. counterterrorism officials see as an emerging threat for the American homeland. They're disparate, confused, Internet-savvy, eager for self-promotion and hard to find. Their very anonymity is frightening, to the point that one Middle East expert worried aloud last week, after the still puzzling Chattanooga murders by Muhammad Youssef Abdulazeez, that America was "one attack away" from a national furor about the lone-wolf threat.

Terror, of course, is precisely what these Internet recruiters want to generate. But U.S. officials caution that the best response is calm, steady work by police and intelligence agencies and a resilient public. "It's a problem we'll have for the foreseeable future," says one official who deals closely with the problem. "The U.S. is much better off than other parts of the world, but we have a lower threshold [of pain]."

After the Chattanooga attack, the administration from the top down warned that the problem doesn't have quick or easy fixes. Officials admit that the best measures are the simplest — communities watching for signs that may predict violent behavior, and a public that doesn't panic when attacks come.

FBI Director James Comey was frank this week in Salt Lake City about the "troubled souls" the online jihadists are trying to mobilize. "Their message is travel to the Caliphate, their so-called Islamic wonder world. Join us here in Iraq or Syria, and if you can't travel, kill somebody where you are. Kill somebody in uniform, preferably in the military or law enforcement, but just kill somebody."

Comey isn't exaggerating. On May 24, an Islamic State fighter calling himself Abu Awlaki tweeted: "I don't understand my ikwa [brothers] in the west. How can u walk past a police officer without stabbing him?"

In these jihadist postings, the brutal call to war is mixed with fantasies that might be drawn from a video game. That's one reason some U.S. counterterrorism experts such as Michael Leiter, former head of the National Counterterrorism Center, don't often use the phrase "lone wolves." They prefer "lone offenders," which doesn't play into the jihadists' self-dramatization.

What troubles U.S. officials is the problem Comey has described as "going dark." He says the FBI can't break the strong encryption that communications and IT companies are offering users. He told Congress this month that he doesn't want greater surveillance authority, but rather technical help from IT companies to access encrypted information "to ensure that we can continue to obtain electronic information to keep us safe." This presumably means "back doors" for decryption, which many companies resist.

The new lone-wolf era will test America's ability to balance security and civil liberties, hopefully more wisely than was the case in the overreaction after Sept. 11, 2001. It's a delicate task. More attacks will drive new calls to crack down through surveillance and more aggressive policing creating more jihadists.

The jihadists' tech skills are undeniable. Nearly every day, the SITE Intelligence Group translates new postings offering tutorials on encryption, phishing, secure messaging and other tools. One techie has even created an Islamic State version of the online game "Flappy Bird."

Here's a taunting message tweeted this month by a jihadist named Kacamack: "where you are with whatever tool you have at your disposal. Or is it that you are all just talk and no walk?"

The right response to these taunts, say U.S. officials, is to keep cool and avoid playing the terrorists' game.

Washington Post Writers Group