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Antivirus firms have identified the main malware behind a major internet attack that hit corporate computer networks in South Korea on Wednesday afternoon. However the source and motives behind the attack remain a mystery. Researchers have dubbed it DarkSeoul.

Computer networks at three South Korean TV stations and at least two major banks - Shinhan and NongHyup - were crippled by data-wiping malware. Internet banking and ATM services at Shinhan Bank were reportedly affected by the surprise assault. Broadcasters KBS, MBC and YTN remained able to stick to their programming schedule despite being left with many hobbled PCs.

At around the same time the website of Korean network provider LG U+ was defaced by the "Whois Team." The defacement featured a picture of three skulls together with alongside a taunting message that stated "User Accounts and All Data are in Our Hands. Unfortunately, We have deleted Your Data. We'll be back Soon."

LG U+ provided internet services for at least some of the firms involved and may have been a conduit in the attack.

The malware at the centre of the attack, dubbed DarkSeoul by Sophos and Jokra Trojan by Symantec, is not particularly sophisticated. "Sophos products have been able to detect the malware for nearly a year, and the various commands embedded in the malicious code have not been obfuscated," the antivirus firm reports.

Sophos said that DarkSeoul/Jokra attempts to disable two popular antivirus products developed in South Korea - AhnLab and Hauri AV. An analysis by South Korean antivirus firm AhnLab fails to mention this but does explain the data-wiping behaviour of the malware in some depth.

The malware "is a simple piece of code that overwrites the MBR (Master Boot Record) making the affected system unable to start after reboot", according to security tools firm AlienVault. AlienVault reckons a Chinese Exploit Kit named GonDad might have been involved in the spread of a family of related data-wiping malware. According to the security firm, Korean domains used to serve this exploit pack were registered using a Chinese email address. But hackers could easily have bought both the exploit kit and the email addresses from underground black markets so this doesn't really prove anything.

Zombie attack?

The speed at which the attack spread suggests that the wiper malware might have been distributed to already compromised clients in a zombie network, although AlienVault's Jaime Blasco is careful to note that his suspicion that a botnet was involved in the spread of the wiper malware remains only a theory.

Simon Edwards of AhnLab noted that a single Chinese IP address is being linked to the South Korea cyber-attack in some local reports. While the source of the attack remains unclear, restoration operations are underway, according to Edwards. He added that most locals appear to view the attacks as a continuation in the escalating tensions between North and South Korea over recent weeks following successful nuclear and rocket tests by Pyongyang.

A separate analysis by Symantec - which detects the same malware as the Jokra Trojan - has revealed that the malware contains a module for wiping Linux machines as well as the capability to wipe Windows PCs. The malware wipes the hard disks of infected computers and send them into a reboot, rendering them unusable in the process. The Jokra Trojan also attempts to wipe any drives attached or mapped to the compromised computer.

"While there are currently no indications of the source of this attack or the motivations behind it, it may be part of either a clandestine attack or the work of nationalistic hacktivists taking issues into their own hands," Symantec explains in a blog post, which also notes some similarities between the South Korean malware and the Shamoon attack against the corporate PC networks of Saudi Aramco and Qatari gas giant RasGas last year.

Meanwhile Trend Micro compares the behaviour of the MBR wiping malware to that of some strains of ransomware.

Both North and South Korea reportedly have maintained cyberwarfare units for several years. Five years ago, South Korea's military command and control centre was the target of a spyware attack from North Korea's electronic warfare division. The Mata Hari character at the centre of the case was convicted of seducing army officers in exchange for military secrets and jailed for five years.

A year later, in 2009, a massive DDoS attack crippled 26 South Korean and foreign governmental websites, including military sites. And two years after that, in 2011, the so-called "Ten Days of Rain" distributed denial-of-service [DDoS] attacks hit multiple government sites as well as the ground, air and naval divisions of the US armed forces stationed in South Korea.

Last week North Korea blamed the US and its allies for computer hacking attacks against its computer networks. ®

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