A malicious hacking crew, possibly based in South Korea, has been quietly stealing data from business executives staying in luxury hotels around the world using a somewhat puzzling mix of highly sophisticated and rudimentary approaches.

The data thefts have been ongoing for at least four years, though there are signs that they began even earlier, security vendor Kaspersky Lab said in a report released Monday. Victims of the Darkhotel malware crew include CEOs, sales and marketing directors, top research and development staff and other senior executives staying at hotels in the Asia-Pacific region.

Who Are the Victims?

Many of the victims appear to have been specifically targeted, which suggests the attackers knew of their travel plans or were looking for them specifically on hotel networks, Kaspersky reported. In most attacks, the cybercriminals have typically compromised a hotel Wi-Fi network first and then waited for their target to log in to it.

Targeted victims who log in to a compromised hotel network using their last name and room number are tricked into downloading and installing a digitally signed back door on their systems. The Darkhotel malware is usually disguised as an update for a legitimate software application such as Adobe Flash, Messenger or Google Toolbar. Once installed, the back door is then used to download other malware tools on the compromised system, including a highly sophisticated, digitally signed keylogger.

How the Darkhotel Malware Works

The Darkhotel malware tools are used to collect a variety of data elements from the compromised systems, such as the details of any antivirus software installed on them and any passwords or other login data cached in Internet Explorer, Chrome and other browsers. Victims potentially stand to lose personal data, sensitive information and intellectual property related to their business.

“The crew never goes after the same target twice; they perform operations with surgical precision, getting all the valuable data they can from the first contact, deleting traces of their work and melting into the background to await the next high-profile individual,” Kaspersky said in its initial announcement.

Many of the victims and hotels that have been compromised are based in Asia, Kaspersky said, adding that it currently has no estimate of how many people may have been affected by Darkhotel.

According to Kaspersky, the Darkhotel advanced persistent threat (APT) crew appears to be highly sophisticated, with a demonstrated ability to compromise, misuse and maintain access to secure hotel networks without being detected. One example of the sophistication displayed by the Darkhotel malware crew is its ability to generate fake digital certificates by reverse-engineering weak keys. Over the years, the group has also occasionally exploited zero-day vulnerabilities, including a recent one in Adobe Flash, to sustain some of its larger campaigns.

Attacks Remain Inconsistent

However, Darkhotel’s malicious activity can also be inconsistent, Kaspersky noted. In some cases the attackers have clearly targeted their victims, while in others they have employed peer-to-peer file-sharing networks to widely deploy the malware.

“The mix of both targeted and indiscriminate attacks is becoming more and more common in the APT scene, where targeted attacks are used to compromise high-profile victims, and botnet-style operations are used for mass surveillance,” Kaspersky said.

In a recent personal interview, Richard Stiennon, chief research analyst at IT-Harvest, said all signs point to a nation-state being behind the attacks.

“Most hotel chains have deployed technology to protect themselves from cybercriminals seeking access to their payment processes and the normal hygiene of AV and patch management,” Stiennon said.

“Stopping the most sophisticated attacks requires continuous monitoring of network activity, full packet capture, security analytics and malware reverse-engineering,” he said. “I know of no member of the hospitality industry that has this ability deployed to their properties.”