Russian intelligence service, the GRU, has been accused of launching a cyber attack on the global chemical weapons watchdog which is investigating the Salisbury nerve agent attack. They are all GRU officers.
Moscow has angrily dismissed the allegations - saying they were part of the West's "spy mania".
The Dutch government on Thursday accused Russia's military intelligence agency, the GRU, of targeting the world's chemical weapons watchdog, the Organisation for the Prohibition of Chemical Weapons, through a cyber operation.
A joint statement from British Prime Minister Theresa May and her Dutch counterpart Mark Rutte said the alleged plot demonstrated "the GRU's disregard for global values and rules that keep us all safe".
Equipment in the auto boot was pointed at the OPCW and was being used to intercept login details, he said, adding that the antenna for the operation lay under a jacket on the car's rear shelf.
It was around this time investigations into the Skripals' novichok poisoning were taking place. Some of their mobile phones were also activated in Moscow near the agency's headquarters.
Ms Bijleveld also accused the men of attempting to access investigation files related to the shooting down of Malaysian Airlines flight MH17 over Ukraine.
It was also reported that the two agents had been planning to travel on to the OPCW-registered laboratory in Spiez near Berne.
The Dutch authorities released CCTV imagery of the four men arriving at Schipol Airport as well photographs of their passports.
They are said to have had €20,000 and $20,000 in cash with them.
Russian Foreign Ministry spokeswoman Maria Zakharova denies the latest allegations of Russian hacking attempts.
"Where Russia acts in an indiscriminate and reckless way, where they have done in terms of these cyberattacks, we will be exposing them", British Defense Secretary Gavin Williamson said Thursday at a meeting with Defense Secretary Jim Mattis and other North Atlantic Treaty Organisation defense ministers in Brussels.
Seven GRU officers allegedly hacked 250 athletes from 30 countries and antidoping organizations, as well as a USA nuclear power company and the Organisation for the Prohibition of Chemical Weapons in the Hague.
According to the indictment, operations were running from December 2014 until at least May this year, and involved "persistent and sophisticated computer intrusions" based on strategic interest to the Russian government.
Three of the seven spies have previously been charged by Special counsel Robert Mueller in his ongoing investigation into Russian interference in the 2016 presidential election.
They said: 'The GRU's reckless operations stretch from destructive cyber activity to the use of illegal nerve agents, as we saw in Salisbury.
Britain and Australia on Thursday blamed Russia's military intelligence service for some of the biggest cyber attacks of recent years - including one on the Democratic National Committee during the 2016 United States presidential campaign.
Through the use of spearphishing emails, stolen credentials and other cyberintrusions, a group calling itself the "Fancy Bears' Hack Team" publicized medical information and drug testing results of athletes and peddled a false narrative that certain athletes were using performance-enhancing drugs, prosecutors alleged Thursday.
The Russian Foreign Ministry on October 4 described the accusations as "fantasy", as British Defense Secretary Gavin Williamson condemned Russia as a "pariah state" whose "reckless and indiscriminate" attacks had left it isolated in the worldwide community. "And that's what happened today", he told reporters in Saskatchewan.