ISIS is using the PlayStation 4 network to recruit and plan attacks because it is 'more secure than WhatsApp' intelligence experts warn, as special forces are deployed on the streets of London with Britain on terror alert.

The move is the biggest security response since the 2005 London bombings and comes after the sickening attacks in Paris on Friday night - the deadliest in Europe since the Madrid bombings in 2004 - that left at least 129 people dead.

In Belgium, which appears to be at the heart of the terror plot, officials believe terrorists are using consoles to communicate.

Belgian Minister of Home Affairs Jan Jambon said intelligence agencies have discovered evidence of jihadis using the games consoles to exchange messages with a special, hidden recruitment channel.

He said: 'Playstation 4 is even more difficult to monitor than WhatsApp.'

ISIS fanatics are also said to be using a 'cyber caliphate' - protected by their own encryption software - where they plan their next attacks.

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Armed City of London Police were clearly visible as participants during yesterday's Lord Mayor's show as Britain beefed up its security

There was a visible increased security with armed police officers stationed at St Pancras station today

Special forces have been deployed to some of London's landmarks and busiest spots, including the Eurostar

Meanwhile, special forces have been deployed to some of the capital's landmarks and busiest spots in the aftermath of the Paris atrocities.

Eighty-nine people were killed after gunmen burst into the Bataclan concert hall and took hostages before security forces stormed the hall.

People were shot dead at restaurants and bars at five other sites in Paris. At least 352 people were injured, of which 99 are critical. ISIS has claimed responsibility.

It is believed two of the bombers were carrying Syrian and Egyptian passports. At least two others are thought to be French while several could also be Belgian.

Last night it emerged French detectives questioned one of the jihadis behind Friday's terror attacks as he crossed the Belgian border and let him go after he showed them his ID card.

Officers pulled over Salah Abdelslam on Saturday morning on the A2 motorway between Paris and Brussels in a hired car used in the attacks.

Detectives soon discovered their blunder when they found Abdeslam had rented a hire car abandoned near the scene of the massacre inside the Bataclan theatre.

However, by the time they alerted Belgian authorities, he had abandoned the car in the jihadi stronghold of Molenbeek in Brussels - the so-called 'den of terrorism' - and disappeared.

An international manhunt has been launched.

French soldiers patrol at the Eiffel Tower today, which remained closed on the first of three days of mourning

Tourists sites in Paris remained shut today following the worst terrorist attack in Europe since 2004

Soldiers from the 3rd Marine Infantry Parachute Regiment of Carcassonne, arrive at Toulouse Blagnac Airport before leaving for Paris as France stepped up its security

THE VITAL CLUES MISSED IN EUROPE BEFORE THE MASSACRE A series of vital clues appear to have been missed that could have averted the Paris atrocities. Iraqi intelligence warned US-led coalition countries of an imminent assault the day before the Paris attacks, it has emerged. At least one of the terrorists was a Parisian who had been on a terror watch list for five years, but was not being monitored closely enough to be stopped before he took part in the murderous attack. Greek authorities believe that two of the gunmen sneaked into Europe posing as a refugee from Syria – heightening fears that not enough security checks are being carried out on migrants. In May this year, The Mail on Sunday revealed the concerns of security analysts that Islamic State extremists were being smuggled into Europe among refugees crossing the Mediterranean. More than a week ago, a heavily-armed suspect was stopped in Germany on his way to Paris. Hidden in his car, police found a terrifying arsenal, including seven Kalashnikov assault rifles and seven hand grenades. The destination programmed into his satnav system was Paris but officers failed to alert anti-terror police. The 51-year-old driver, a Muslim from Montenegro, was arrested and held in custody but has refused to talk. In August, French intelligence detained a 30-year-old man on his way back from Syria who said militants were planning attacks on French concert halls. Prosecutors also said the terrorists used an improved explosive known as TATP, or triacetone triperoxide, which also was used in the 2005 bombings in London and were likely to be homemade with ingredients usually traced by the secret services. French intelligence and security services had been reorganised in the wake of the Charlie Hebdo massacres, which left 16 dead in January. A former senior intelligence officer very familiar with France said he and a lot of French intelligence officials think that after two internal services — the Central Directorate of General Intelligence (RG) and the Directorate of Territorial Surveillance (DST) — were merged, it created a larger, but far weaker, General Directorate for Internal Security. Alain Charret, an expert on France's surveillance system, said it was hard for the military to be everywhere and for intelligence to predict everything, 'but the reason why it is usually difficult to track people is because one or two people on their own are involved — here, it seems like it was a big group of organised people, so it should have been tracked more easily.' Advertisement

At least one of the attackers is believed to have passed through Greece as a refugee.

Meanwhile, it has been revealed that around 250 jihadists have returned to France from Syria - but the number coming back to Britain is almost double that.

Experts have also said there are as many as 2,000 people 'of interest' in the UK to MI5 and security services.

Speaking on Newsnight, BBC Correspondent Richard Watson said: 'In France, ten people per week for the last five months have travelled to Syria and many of them have come back.

'In the UK, 760 people are assessed to have travelled out to Syria. Sixty people are assessed to have died fighting in Syria and half are back in the UK already.

'There are 2,000 people of interest in the UK to MI5 and security service. The question is how do you keep tabs on 2,000 people?'

He also explained how the ISIS fanatics were using a 'cyber caliphate' - protected by their own encryption software - where they plan their next attacks.

He said messages between ISIS supporters following the French attacks urged them to 'act when you're ready', 'wait for the word' and that the UK was 'very hot' with police action so said they should 'bide your time and wait until your safe'.

Another security expert has said the government is 'two or three steps' behind ISIS terrorists who are using encrypted computer software and 'burning' messages to avoid detection.

Large numbers of ISIS fighters are young, highly educated Westerners who are fighting the holy war with sophisticated backgrounds and training with digital technology.

Militants' use of Twitter and Facebook allows them to target an entire new generation of young possible recruits, while the beheading videos of James Foley and Steven Sotloff were created using skilled video and audio editing techniques.

Security Expert Will Geddes told MailOnline: 'They are using various different encrypted messaging apps [such as Kik, Surespot, Wickr and Telegram] that cannot be hacked even by secret services.

'The messages they send also have a burn time which means they will be deleted after a certain time so will not show up on a phone.

'This allows them to remain under the threshold of detection and it's becoming increasingly difficult for security services.

'Security services have to get permission from the app if they want to access the data, but many of the apps have an obligation where they need to notify the user that a request for communication has been made.

'This gives them a heads up and they can then move to another app. We are two or three steps behind them.'

He added: 'These messages will include details of the planning stage but then, more critically, when they are at the last stage in preparations for attack and seeing whether everyone is in position.'

The Investigatory Powers Bill, which was published in draft form a fortnight ago by Home Secretary Theresa May, will force internet firms to hand over to MI5, MI6 and GCHQ messages sent on apps and other encrypted services.

The escalating threat posed by ISIS was highlighted in a speech last month by MI5 chief Andrew Parker who warned the group wanted their attacks to kill a maximum number of people.

French fire officer helped an injured man away from the scene of the attack at the Bataclan concert in Paris on Friday night

Some people tried to escape from the carnage by clambering down the outside of the concert hall and by crawling over dead bodies - a pregnant woman was left hanging from the window

PARIS MASSACRE: WHAT WE KNOW SO FAR ABOUT DEADLY TERROR SIEGE At least 129 people are dead, and another 352 injured, after three teams of jihadis struck the Stade de France football stadium, a handful of bars and cafes, and then finally the Bataclan concert hall. FIRST TWO ATTACKS: STADE DE FRANCE The attacks began at 8.17pm GMT at the Stade de France where the French football team was hosting Germany in an international friendly.

The game was being watched by 80,000 spectators, among them was President Francois Hollande who had to be evacuated from the stadium.

The first explosion, a suicide bombing, was at an entrance to the stadium. A suicide bomber approached the gate with a match ticket when he was frisked by a security guard who turned him away.

He backed away from the gate and detonated his vest at about 8.20pm GMT near Gate D of the stadium, killing one other person. A passport with the name Ahmed Almuhamed, 25, from Syria, was allegedly found nearby.

A second suicide bomber, Bilal Hadfi, 20, blew himself up near Gate H several minutes later. No one else was reported killed. Hadfi is said to have fought with ISIS in Syria. THIRD ATTACK: LE PETIT CAMBODGE AND LE CARILLON BAR At 8.25pm GMT a separate team of gunmen arrived in a Black Seat and attacked diners at popular Cambodian restaurant Le Petit Cambodge and Le Carillon bar in the trendy Canal Saint-Martin area of eastern Paris, killing 15. Timeline of events: Eight bombers carried out the devastating attacks on Friday night, leaving 129 people dead and another 352 injured FOURTH ATTACK: LA CASA NOSTRA PIZZERIA AND LA BELLE EQUIPE BAR The same unit then drove about 500 yards to La Casa Nostra pizzeria and opened fire on diners on the terrace of the restaurant, killing at least five people.

From there, the militants drove around a mile south-east – apparently past the area of the Bataclan concert venue – to launch another attack, this time on La Belle Equipe bar in Rue de Charonne. At least 19 people died after the terrace was sprayed with bullets at 8.38pm GMT. The attackers then drove off. FIFTH ATTACK: CAFÉ 'COMPTOIR VOLTAIRE' Five minutes later, Ibrahim Abdeslam, 31, set off a suicide vest outside the outside cafe 'Comptoir Voltaire' on the Boulevard Voltaire and close to the Bataclan theatre. He hired a black Seat car used in the attack. SIXTH ATTACK: BATACLAN MUSIC HALL At 8.49pm GMT, the third group (believed to be three men and a woman) armed with AK-47s stormed the Bataclan music hall and began shooting members of the crowd. Survivors claim three blew themselves up and a fourth person was shot dead by police before they could detonate their bomb. SEVENTH ATTACK: NEAR STADE DE FRANCE At around 8.50pm GMT a third blast took place near the Stade de France, this time by a McDonald's restaurant on the fringes of the stadium. The boom caused terror among spectators who had already been attempting to flee the stadium following the first two explosions. The attacker who detonated his suicide vest was identified as a 20-year-old French man living in Belgium. Tearful members of the public view flowers and tributes on the pavement near the scene of the concert hall massacre on Friday AFTERMATH: On Saturday morning, ISIS claimed responsibility for the attacks across Paris, saying 'eight brothers wearing explosive belts and carrying assault rifles' conducted a 'blessed attack on... Crusader France'.

On Saturday afternoon, three people travelling in a grey VW Polo were arrested at the French/Belgian border when police traced the car after it was sighted outside the Bataclan theatre at the time of the attacks.

One of the Stade de France suspects was found carrying a Syrian passport under the name Ahmed Almuhamed who travelled to France as a migrant through Greece on October 3. Ferry tickets reveal he travelled with another man named as Mohammed Almuhamed.

However, the French minister of justice Christiane Taubira said on Sunday that the passport under the name Ahmed Almuhamed was a fake.

Omar Ismaël Mostefai, 29, from Courcouronnes, Paris was also named as a Bataclan suicide bomber. The petty criminal and father-of-one was known to police as a radical and had travelled to Algeria and Syria. He was identified by the fingerprint on a severed digit found after he detonated his suicide belt.

Mostefai is believed to have been radicalised by a Belgian hate preacher of Moroccan descent claimed to have regularly preached at his mosque in South West France. His father, a brother and other family members have been held and are being questioned.

The black Seat Leon used by the terrorists who murdered diners outside the Casa Nostra pizza restaurant and the La Belle Équipe cafe was found abandoned 20 minutes away in Montreuil with a cache of weapons inside.

Seven people were detained in Belgium linked to the atrocities - three at the border and four in Brussels. Five are from the Molenbeek area of Brussels known as a 'den of terrorists'.

Iraqi spies warned the West of an ISIS suicide bomber threat the day before the Paris atrocities, it was revealed on Sunday, as more details of major intelligence failures began to emerge. The US-led coalition in Syria was apparently told by Iraqi security sources that 24 extremists were involved in the terror operation planned in the ISIS capital Raqqa and it would involve 19 attackers including five others including bombmakers and planners. No detail was given of when or where an attack might take place.

It has also emerged that Turkey's authorities foiled a plot to stage a 'Jihadi John revenge attack' in Istanbul - involving a high-profile British jihadist - on the same day as the deadly massacre in Paris.

From as far back as August, France's authorities possessed information that militants were said to be planning attacks on French concert halls after a tip-off was received from a 30-year-old man who was detained on his way back from Syria.

On Sunday night there were 42 people still said to be in intensive care in hospital following Friday's terrorist attacks. LATEST DEVELOPMENTS: French police are still hunting for three gunmen on the run, including Brussels-born Frenchman Salah Abdeslam, and an ISIS bombmaker likely to have made the suicide vests.

An international arrest warrant has been issued for Abdeslam, 26, who is accused of renting a Volkswagen Polo used by the suicide bombers. He is one of three brothers believed to be at the heart of the eight-strong ISIS cell.

It emerged on Sunday night that police found Abdeslam near the Belgian border early Saturday but let him go after he showed them his ID card. Officers pulled over the car being driven by Abdelslam on Saturday morning on the A2 motorway between Paris and Brussels. Two other men were also in the Seat car. At the time, officers in Paris knew that Abdeslam had rented the car used by the killers which had been abandoned near the theatre but the information had not been transmitted to those responsible for conducting the border checks.

His brother Ibrahim, 31, blew himself up in a solo attack outside cafe Comptoir Voltaire after renting a black Seat found abandoned today filled with AK-47s and ammunition. A third sibling, named as Mohamed Abdeslam, has been arrested in the Belgian capital.

On Sunday evening the French defence ministry announced that the country's warplanes had bombed Islamic State's stronghold in Syria's Raqa, destroying a command post and a training camp, the defence ministry said. Ten fighter jets were involved, dropping 20 bombs. Advertisement

In a rare public speech he said: 'We have seen greater ambition for mass casualty attacks. All of this underlines the growing threat we face.'

He added: 'It may not yet have reached the high water mark, and despite the successes we have had, we can never be confident of stopping everything.'

Charles Farr, director of the Office for Security and Counter-Terrorism, said ISIS was inspiring people in Britain who 'couldn't go' to its territories in Syria or Iraq to stay and 'undertake attacks.'

Mr Farr said the ISIS ideology and call was either to go and 'join the so called Islamic State' or stay and 'undertake attacks if you couldn't go', the Daily Telegraph reported.

He said this was a 'specific, singular and new phenomenon of ISIS,' a form of 'ideological grooming' of young people and a distinct ideological shift from previous Islamist inspirations.

David Cameron said the terror threat level in the UK would remain at 'severe' but the Paris attack would prompt a review of plans and suggested the threat posed by ISIS was 'evolving'.

Patrols and security measures are also being stepped up across Europe and in the US following the Paris attacks.

There was a heavy police presence at the French-German border and in France the Eiffel Tower and other popular tourist spots have been shut down with hundreds of armed soldiers guarding key sites.

In the US, heavily-armed officers stood guard in Times Square and extra security was sent to French government sites in New York, Boston and Washington.

Candles were light today in the French capital after the terrorist attack that left 129 dead and 352 injured