Researchers have uncovered an advanced malware-based operation that siphoned more than 600 gigabytes from about 70 targets in a broad range of industries, including critical infrastructure, news media, and scientific research.

The operation uses malware to capture audio recordings of conversations, screen shots, documents, and passwords, according to a blog post published last week by security firm CyberX. Targets are initially infected using malicious Microsoft Word documents sent in phishing e-mails. Once compromised, infected machines upload the pilfered audio and data to Dropbox, where it's retrieved by the attackers. The researchers have dubbed the campaign Operation BugDrop because of its use of PC microphones to bug targets and send the audio and other data to Dropbox.

"Operation BugDrop is a well-organized operation that employs sophisticated malware and appears to be backed by an organization with substantial resources," the CyberX researchers wrote. "In particular, the operation requires a massive back-end infrastructure to store, decrypt, and analyze several GB per day of unstructured data that is being captured from its targets. A large team of human analysts is also required to manually sort through captured data and process it manually and/or with Big Data-like analytics."

Examples of targets infected in the campaign include:

A company that designs remote monitoring systems for oil and gas pipelines

An international organization that monitors human rights, counter-terrorism, and computer attacks on Ukrainian critical infrastructure

An engineering company that designs electrical substations, gas distribution pipelines, and water supply plants

A scientific research institute

Editors of Ukrainian newspapers

Most of the 70 organizations known to have been infected in Operation BugDrop are located in Ukraine, a country that in December suffered a hacker-caused power outage . It came almost exactly a year after a 2015 attack on Ukraine's power grid that caused 225,000 residents to lose electricity. In both cases, the power facilities had been hacked weeks or months before the outages so that attackers could gather passwords for targeted servers and workstations and create custom malware for them. CyberX CTO and cofounder Nir Giller told Ars that the campaign siphoned at least 600 gigabytes of data from its targets. Other countries affected included Saudi Arabia and Austria.

There's no evidence that the same attackers are responsible for both Operation BugDrop and the Ukrainian power outages. Still, similarities abound. Both targeted a broad range of industries in the same geographic region. And both relied on e-mails that tricked targets into enabling malicious macros included in Microsoft Word documents. CyberX researchers said Operation BugDrop also bears similarities to a surveillance campaign known as Operation Groundbait that was uncovered last May. Operation BugDrop, however, is noticeably more advanced than Operation Groundbait, and CyberX researchers said they don't know if the two are unrelated or if Operation BugDrop was created after Operation Groundbait became public.

Some examples of the way Operation BugDrop is more sophisticated include:

Dropbox for data exfiltration. Organizations typically don't prevent end users from accessing Dropbox and often don't monitor connections. That helped the surveillance operation to remain stealthy.

Reflective DLL Injection, a malware injection technique that was also employed by the BlackEnergy malware used in the Ukrainian power grid attacks and by Duqu in the Stuxnet attacks on Iranian nuclear facilities. Reflective DLL Injection loads malicious code without calling the normal Windows API.

Encrypted DLLs that avoid detection by common anti-virus and sandboxing systems.

The use of legitimate free Web hosting sites for command-and-control infrastructure. The hosting sites required little or no registration information, making it hard for researchers to learn much about the attackers.

To become infected, targets had to open the malicious Word document attached to the phishing e-mail and enable macros. To increase the chance targets would change this default setting, the Word document included a graphic that looked like an official Microsoft notification. It read: "Attention! The file was created in a newer version of Microsoft Office programs. You must enable macros to correctly display the contents of a document."

CyberX researchers stopped short of identifying a specific country involved but said Operation BugDrop was almost surely the work of a government with nearly limitless resources.

"Skilled hackers with substantial financial resources carried out Operation BugDrop," they wrote. "Given the amount of data analysis that needed to be done on [a] daily basis, we believe BugDrop was heavily staffed. Given the sophistication of the code and how well the operation was executed, we have concluded that those carrying it out have previous field experience."