LONDON — ISIS has just claimed responsibility for Saturday night’s deadly terrorist attack here, which killed seven people and badly wounded dozens more. The move came a day after British police arrested 12 people in the nearby suburb of Barking who may have connections to the strike.

It’s worth being a bit skeptical of the terror group’s claim. ISIS has recently claimed responsibility for incidents, like a shooting in the Philippines last week, that turned out to have nothing to do with them.

But even if the ISIS claim turns out to be false, that shouldn't be taken as reassuring. The London Bridge attack — in which three still-unnamed men armed with solely knives and a van managed to kill seven and wound 48 in just eight minutes — represents the new face of the global terrorist threat.

This kind of attack doesn’t involve a major 9/11-style plot, which take years of planning, communications, and money transfers, making them potentially easier for law enforcement authorities to detect and stop.

Instead, it’s a style of attack that’s small-scale, and easy for deranged individuals to carry out on their own with no advance planning or assistance from (let alone communication with) an outside group like ISIS.

The London Bridge attack appears to be a direct copy of an attack on London’s Westminster Bridge in March, where a man mowed down pedestrians and then stormed Parliament armed with a knife, killing five people. It also comes on the heels of late May’s suicide bombing at an Ariana Grande concert in Manchester, which killed 22.

UK police, like their American counterparts, are seriously worried about these attacks inspiring other violent individuals, leading to a constant drumbeat of terrorist violence.

“We are dealing with people who appear very volatile, very unstable many of them. People who are prepared to use low-tech methods and sometimes go from thinking about the idea to carrying out an attack in a very short space of time,” Cressida Dick, the commissioner of London’s Metropolitan Police, said in a Monday morning appearance on the UK’s Today Show. “This is very, very challenging.”

These attacks aren’t undetectable: UK police have apparently disrupted five domestic terrorist plots since March. But they are hard enough to stop that some attackers will get through.

The Westminster Bridge attack involved only one man, British national Khalid Masood. People like Masood are what terrorism experts call “lone wolves” or “lone operators.” They decided to plan and execute the attacks entirely on their own, without participation from either a radical network or co-conspirators. That supercharges the problem of detection created by low-level terrorism more broadly, as police are even less likely to get advance warning about the attack.

"Attacks by lone operator terrorists provide the most puzzling and unpredictable form of terrorism," Edwin Bakker and Beatrice Graaf, terrorism scholars at the University of Leiden, write in Perspectives on Terrorism. "Lone wolf terrorists are a nightmare for the counterterrorism organizations, police and intelligence communities as they are extremely difficult to stop."

All-in-all, the spate of attacks we’ve seen in the UK is posing an extraordinary challenge for UK police — one that doesn’t appear to being fading.

“[Counter-terrorism] professionals have wondered for over a decade why we haven't seen more terror attacks like this,” explains Will McCants, a senior fellow at the Brookings Institution. “Now that they've arrived, they're not going away any time soon.”

Why this kind of attack is so easy to execute

The basic mode of attack used in London — ramming a crowded area with a vehicle, then getting out and stabbing anyone you can find — can be easily carried out with no direction from experienced militants. All it takes is a car, a knife, and a willingness to kill, and potentially die, for your beliefs.

It doesn't require direct communication with a major terrorist group, or money or other forms of assistance from the organizations. ISIS in particular has encouraged would-be militants who share their beliefs to carry out as many strikes as they can in their home countries without consulting ISIS HQ in Syria first. Both ISIS and al-Qaeda propaganda have specifically told these attackers to use cars as weapons.

“Terrorist groups now push out this methodology that you should use whatever the hell you have to hand to kill whoever the hell you can find,” says Raffaello Pantucci, a counterterrorism expert at the Royal United Services Institute, a London-based think tank. “That makes it very difficult for security services to stay ahead of that.”

Why is it so hard? Simple attacks, disconnected from any international or well-known terrorist cell, give off few of the signatures that would help detect the attack in advance.

“There's just no way to stop them if a person is not part of a known group”

To disrupt a terrorist plot, law enforcement and intelligence agencies need, well, intelligence: an informer with knowledge of the plot, intercepted communications between the plotters, etc. It’s hard to catch that if people are acting alone, or in a tight-knit group that doesn’t contain anyone currently under police surveillance.

That doesn’t make this kind of plot impossible to prevent. In April, British police arrested a suspected jihadist named Khalid Mohammed Omar Ali while he was carrying several knives. Ali was on his way to Downing Street, where the UK’s equivalent of the White House is located, but had been under surveillance for some time. According to some reports in the British media, the police had been tipped off by Ali’s family, who had become worried about his behavior.

This is not uncommon. According to Pantucci, research on terrorists finds that they typically do tell at least one person what they’re planning on doing. But “typically” doesn’t mean always — and even then, the person or people they tell might not take it seriously, might not have enough advance warning, or just plain may not trust the police. If enough people attempt attacks like the one on London Bridge, which are confined to a small group and involve relatively little planning, some of them will inevitably get through.

“There's just no way to stop them if a person is not part of a known group,” as McCants puts it.

The special danger of “lone wolves”

We don’t yet know how involved the 12 people arrested in Barking were — at least one person detained in that raid has been released — but the London Bridge strike involved more attackers than the Westminster Bridge incident and may have thus had a larger circle of people who knew about or provided some support. Westminster-style lone wolf attacks are even harder to predict.

There’s no set profile for lone wolf terrorists; they come from all sorts of ethnic, class, and social backgrounds. Unlike most terrorists, they do not seem to have a deep and sincere belief in Islamist ideology: A survey of 119 lone wolf terrorists by the University of London's Paul Gill found that many of these attackers were mentally ill or relatively isolated socially.

That’s not the case for militants who participate in more organized plots, many of whom are decently well-off personally. It appears that many of these lone wolves are simply latching onto extremism when they're really motivated to violence by other factors.

The difficult mash of lone wolf motives is part of why Commissioner Dick sounded so worried in her Monday morning comments. With terrorism becoming a kind of trend in the UK — three attacks in less than three months — these “unstable” individuals, as she put it, may be more likely to be inspired to kill for their own, unfathomable and unpredictable, reasons. London Bridge appears to have been an organized plot, but the next attackers it inspires might not be.

“We are experiencing a new trend in the threat we face, as terrorism breeds terrorism,” UK Prime Minister Theresa May said in a Sunday speech. “Perpetrators are inspired to attack not only on the basis of carefully constructed plots after years of planning and training — and not even as lone attackers radicalized online — but by copying one another and often using the crudest of means of attack.”

What can be done?

There are some measures the UK government can take to help prevent this. Increased police funding, for example, may well have prevented the Manchester attack

“The Manchester attacker himself was reported to the security services at least five times by the local Muslim community, yet was not monitored due to the lack of resources,” Vice’s Aris Roussinos reports.

But this isn’t going to stop every attack. And overreactions — like a proposal offered by May to attempt to restrict “extremist” messaging on social media in the wake of London Bridge — might well play into the militants’ hands.

Lower-level attacks like the one in London, or even the bombing in Manchester, are not designed to cripple a country. The goal, instead, is psychological: The intent is, quite literally, to terrorize. To make anyone think that, at any moment, they might not be safe — that they could be next.

There are any number of reasons that jihadist might want to create this kind of panic.

It could be revenge, punishing Britain for its participation in the coalition fighting ISIS in Syria and Iraq. It could be strategic — provoking British politicians into crackdowns on civil liberties and Muslim rights that would fuel the jihadists’ narrative of a civilizational war on Islam, thus strengthening their recruiting. It could be economic, to scare tourists and investors and thus damage the British economy. It could simply be blind anger, that these people hate Western societies and want to lash out against them.

But panic is certainly the goal. Experts say that, other than patching specific holes like the lack of funding in Manchester, the best thing the government can do is continue to let security services do their jobs — without draconian crackdowns on civil liberties.

“They [security services] have to be doing more of what they’re doing — as we saw in the fact that they disrupted five [plots] in the last months,” Pantucci says. “The difficulty is that it’s very difficult to get everything.”

And that’s what makes this new type of terrorism so scary. Why the casualty count of an individual attack will never approach that of September 11, or even the 2005 bombings on the London Underground (which killed 52 and wounded over 700), the body count will steadily rise as smaller attacks proliferate. And the fear they generate may end up pushing British politics in a direction that’s actively harmful, both to security and to fundamental British values like equality and freedom.

“The British are resilient,” Richard Walton, the former head of the London Police’s counterterrorism unit, tweeted on Sunday. “But 34 killed & 214 injured in 3 terror attacks in under 3 months is testing tolerance.”