Well-known British security researcher Kevin Beaumont was one of the first to point to a statement on on the Spain-based company's website in which it said that there had been "a security information incident on its telecommunications platforms".
Prosegur is the largest security firm in Spain and listed on Madrid Stock Exchange in 1987.
Prosegur appear to be in a hell of a mess, I’ve been monitoring social media posts and staff outside Spain in multiple offices report Ryuk ransomware on systems and outage of all services, so I’m guessing they have a common AD domain.— Kevin Beaumont (@GossiTheDog) November 27, 2019
The company later said the ransomware in question was Ryuk.
In an analysis of the ransomware last year, Check Point's Itay Cohen and Ben Herzog said the encryption scheme used by Ryuk "is intentionally built for small-scale operations, such that only crucial assets and resources are infected in each targeted network with its infection and distribution carried out manually by the attackers".
"This, of course, means extensive network mapping, hacking and credential collection is required and takes place prior to each operation."
“We enacted our security protocols as soon as the incident was detected”. Might be being slightly facetious, but maybe it was an idea to enact those protocols much earlier. (I assume by security protocols they really mean IR/DR)— Matthew Hall (@pentestmatt) November 27, 2019
Beaumont wrote that he had found the ransom payment note and payload on VirusTotal, a site to which researchers upload executables to be scanned by anti-malware engines and detected, if known.
"I found the ransomware payment thing and payload on VT, their PCs started displaying this," he wrote. "I've blanked the email address in case they want to pay. Wishing them a speedy recovery."
Cohen and Herzog said their research had led them to connect the nature of Ryuk’s campaign and some of its inner workings to the HERMES ransomware, a malware commonly attributed to the notorious North Korean APT Lazarus Group