The attackers who unleashed devastating hard-drive wiping malware on South Korean TV stations and banks earlier this week executed at least part of the attack by hijacking the firms' patch management admin accounts, the software vendor involved has said.
According to South Korean antivirus company AhnLab, the 20 March attacks used stolen IDs and passwords for its Patch Manager software to distribute the malware to an unknown number of the 32,000 PCs affected inside the victim firms, including the Munhwa, YTN, Korea Broadcasting System (KBS) TV stations, and the Shinhan, Jeju and Nonghyup banks.
These systems were under the control of the organisations involved and not AhnLab itself, the company emphasised.
"Contrary to early reports, no security hole in any AhnLab server or product was used by the attackers to deliver the malicious code," AhnLab said in a statement.
The fact that several of the firms were using the company's software was coincidence; as a local ISV, AhnLab enjoyed a high market share in the country for its security products, the company said.
Exactly how the attackers were able to get hold of the credentials and co-ordinate the attack remains a mystery but indicated that it had been planned for some time, AhnLab director of marketing and business development Brian Laing said.
Some have suggested that the attackers had gained control of at least some of the target PCs using an undetected botnet system, but this remains speculation.
Laing agreed that the attack had attempted to shut down AhnLab's antivirus client as well as that of a second popular South Korean vendor, Hauri.
Claimed by the mysterious 'Whois' team, the attack attempted - and succeeded - in causing maximum disruption by overwriting the Master Boot Record (MBR) on affected PCs after a reboot.
This is remarkably similar to the 'Shamoon' attack last year on Saudi Arabia's oil industry, which also affected about 30,000 systems after executing its disk-wiping routine at a pre-defined moment.
One unusual element of the South Korean malware, dubbed 'Jokra' by Symantec, is that despite being Windows-oriented it contains a script that could be used to wipe Linux systems.
"The included module checks Windows 7 and Windows XP computers for an application called mRemote, an open source, multi-protocol remote connections manager," a Symantec analysis reported.
Suspicions have fallen on North Korea or another state as the culprit simply because of the resources necessary to pull of such a targeted and highly-crafted attack.
The fact that victims were solely South Korean has also reinforced this view. As with so many cyberattacks, evidence is and will probably remain, thin on the ground.