The BBC reported: "A Dutch journalist managed to gatecrash a confidential video conference of EU defense ministers. Daniel Verlaan of RTL Nieuws joined the meeting after the Dutch defence minister accidentally posted some of the login details on Twitter.
Mr. Verlaan managed to access the meeting after Dutch Defence Minister Ank Bijleveld tweeted a photo that contained the login address and part of the PIN code.
"After a number of attempts, RTL Nieuws succeeded in guessing the PIN code of the secret consultation, because five of the six digits of the pin code were visible in the photo,"
Best as I can tell, one of the participants took a photo of his computer screen and then posted it on Twitter. The meeting access info appears to be in the browser bar (now blackened out) - with 5 of the 6 PIN digits all the way on the right. So it only took 10 guesses max to access this "not so secret meeting"