The changing face of terror means new challenges for the West when individual attackers start acting on their own initiative

The face of terror is changing, and security services across Europe are having to rethink their strategy in the wake of the attack in London. A middle-aged man deliberately drove a car into pedestrians on Westminster Bridge, killing three, before crashing it into railings surrounding the Houses of Parliament, then running on foot brandishing two kitchen knives and fatally stabbing an unarmed policeman. He was then shot dead.

Khalid Masood, in his 50s, had converted to Islam after a life littered by convictions for assault, threatening behavior and other minor crimes. He didn't fit the accepted image of an Islamist extremist. Police and security services are going through his past with a fine-tooth comb for clues. His conversion to Islam from being a sport-loving Kent schoolboy is not in doubt.

Many terror perpetrators are typically young men who have been radicalized by any number of online extremist preachers railing against the West.

Their use of social media, and a readiness by Islamic State extremists to claim their actions as being arranged or inspired by them, often convinces security services of their links to organized terror. After all, getting hold of guns and the ingredients for bombs takes money and organization.

But as the attacks in Nice and Berlin proved, an everyday item such as a vehicle or a humble kitchen knife, which require little organizational skill to procure, is enough to do untold damage.

This has given rise to so-called lone wolf attacks, increasingly difficult for police and security services to monitor and indeed prevent.

The attack on Parliament takes it all one stage further.

One senior police officer interviewed by The Times said frankly that police may never know what really motivated Masood.

Indeed, on March 27, Deputy Assistant Commissioner Neil Basu went even further, saying the police had no evidence that Masood had been in contact with IS and had found no evidence that he had been radicalized in prison in 2003.

Theories in the media abound. He was, it is said, bipolar or even schizophrenic. For such people, the theory goes, all that's needed is a trigger to initiate a psychotic frenzy. All of which means he simply copied similar attacks without being radicalized.

There is one fly in the ointment - Masood apparently sent a message on WhatsApp minutes before he sped his car into the crowds on Westminster Bridge.

Unbelievably Facebook, WhatsApp's owners, are refusing to release the contents of the message, despite demands from British Home Secretary Amber Rudd.

If the contents can be recovered, they may answer the key question - did he have any ties to a terror group?

Security services here and across Europe have developed a sophisticated way of tracking suspects and monitoring their web and social media. In the UK alone, security services say they have prevented 13 active terror plots in the past four years alone.

It has been revealed that MI5, Britain's main counter terror intelligence service, had become interested in Masood in the 1990s, because he had spent a couple of spells teaching English in Saudi Arabia, but nothing concrete about radicalization could be found, and he dropped off the radar.

The attack on Parliament is throwing up more questions by the day that can't easily be answered.

The appearance of the lone wolf fanatic demands a whole new approach from the already hard-pressed security services.

As for us, the great British public, we really do have to keep calm and carry on. And drink tea.

The author is managing editor of China Daily European Bureau. Contact the writer at chris@mail.chinadailyuk.com