Drone incidents at airports and military bases all over Jutland, western Denmark, have not caused any harm or damage - and yet they have exposed the country's defences as vulnerable to attack.
In an era of hybrid warfare, there is a sense of embarrassment in Denmark - a founding member of the North Atlantic Treaty Organization (Nato) alliance - that its critical infrastructure has become so vulnerable.
Aalborg and Billund airports had to close on Wednesday night, while drones were spotted at Esbjerg, Sonderborg and Skrydstrup. Aalborg also serves as a military base and Skrydstrup is home to some of the air force's F-35 and F-16 war planes. Drones were also seen over the Jutland Dragoon regiment at Holstebro.
There have since been reports of police investigating drone activities around Denmark's oil and gas platforms in the North Sea, and near the central port of Korsor.
Aalborg airport briefly closed again on Thursday night following another suspected drone sighting, police and national media said on Friday.
The question now facing the country's military is how to respond.
None of the drones have been shot down - defence chiefs decided it was safer not to, but that is not a long-term solution.
Denmark is, of course, not alone.
Norway, Estonia, Poland, Bulgaria and Romania have all been subjected to hybrid warfare in recent weeks. All are on Nato's eastern flank.
Estonia and Poland have both invoked Nato's Article 4 this month after Russian war planes entered Estonian air space for 12 minutes, and about 20 Russian drones violated Polish airspace and were shot down.
The Danish government is currently assessing whether to invoke it too.
This is a serious moment for Denmark, and its top brass - government, defence and police - quickly called a press conference where Defence Minister Troels Lund Poulsen said it looked systematic, because of the number of locations targeted.
Russia has not been ruled out - something Prime Minister Mette Frederiksen made clear after Monday night's drone disruption over Copenhagen.
Moscow firmly rejects any involvement and its embassy in Copenhagen has denounced the incidents as staged provocation.
However, Frederiksen is in no doubt about the risk and said only last week that Russia will be a threat to Europe and Denmark for years to come.
Denmark's cautious approach is markedly different from Poland's since Russia's drone incursions there on 10 September.
The government recently announced plans for an integrated layered air defence, along with investment in long-range precision weapons to hit enemy territory.
On Friday, Denmark will join several Nato allies and Ukraine to discuss the idea of erecting a drone wall, proposed by European Commission President Ursula von der Leyen, to protect the EU's eastern borders.
The aim is to create an early detection system, although this may not have helped Denmark overnight if drones spotted over Jutland were launched locally.
If Russia was behind the latest drone disruption, despite its denials, then by the standards of hybrid warfare this operation appears to have been a success.
Airports were briefly closed, Denmark's military sites were made to look vulnerable, and senior ministers were forced to give a rushed press conference to allay public concerns.
