Two Austrian YouTubers have published a video they say shows their unauthorised entry into the "Colonel-Pilot Milenko Pavlović" military airfield at Batajnica near Belgrade. The footage shows them climbing on military aircraft and wandering freely around the complex. Nobody asked them what they were doing there.

The video was posted on the "Roofless TV" channel and racked up more than half a million views in a few days. According to the creators, part of the footage was shot in Kazakhstan, after which the action moves to Serbia. The two young men first film the planes from outside, through the fence, and then from inside the military facility itself.

They walked around aircraft that are clearly no longer in use, climbed into some of them and filmed them. At one point they even filmed a plane landing. From the published material, it appears they did not meet a single member of staff the whole time they were on the protected site. How they got in is still unknown.

The channel is run by two young Viennese men who present themselves as explorers of hidden locations. It is known for so-called "urbex" exploration of abandoned and off-limits places, as well as parkour stunts. In other words, this is their trade - and that is exactly why some caution is due: this is their claim and their edit, not an officially confirmed incident.

The problem is what comes next. Serbia's Defence Ministry and police have so far not commented. The Batajnica airfield is about twenty kilometres from Belgrade, was built between 1947 and 1951, and today houses the 204th Air Base of the Serbian Armed Forces' Air Force and Air Defence. If the video is genuine, two lads with a camera strolled through a military air base on Belgrade's doorstep. If it isn't, someone should have come out and said so by now.

Silence is the worst option. When half a million people watch foreigners climbing over military aircraft and the institution that spends money on security doesn't have a single sentence to say, the question is no longer about two YouTubers. What are security assessments worth if the fence of a military airfield can be crossed with a camera in hand - and is anyone in the region checking their own fences right now?