Security researchers have described the malware as among the fastest-spreading mobile threats in recent years.

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Android logo displayed on a smartphone with malware alert in the background
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An international team of law-enforcement officials has successfully disrupted infrastructure associated with FluBot, an especially pernicious malware tool that threat actors have been using since at least December 2020 to steal passwords, bank account details, and other sensitive data from Android users.

Europol announced the takedown Wednesday, noting that FluBot's infrastructure was now under the control of law enforcement.

"An international law enforcement operation involving 11 countries has resulted in the takedown of one of the fastest-spreading mobile malware to date," Europol noted. "The investigation is ongoing to identify the individuals behind this global malware campaign."

Researchers first spotted FluBot (at that time referred to as Cabassous) targeting Android users in Spain in December 2020. Over the course of the next year, the malware spread like wildfire to what Europol described as a "huge number" of Android devices in multiple countries, including Germany, the UK, France, Finland, Australia, and New Zealand.

A Fast-Spreading Viral Threat

FluBot spreads via SMS phishing messages (smishing) that use various pretexts to try and get recipients to click on a link for downloading the malware to their smartphones. In the early days of the malware, the SMS messages purported to be from delivery companies such as FedEx and DHL attempting to drop off a package. Users who were tricked into clicking on the link — ostensibly to reschedule delivery — ended up with the malware, disguised as a mobile app from the delivery company, downloaded to their Android devices.

Once installed, the malware seeks specific access privileges on the device that, if granted, it would use to steal payment-card data, bank account information, and other sensitive data. The malware was also designed to intercept and read text messages, open pages, disable Google Play Protect, and uninstall various apps from an infected device.

In addition, FluBot copies the infected device owner's contact list and sent SMS messages with infected links to all the numbers — a factor that likely contributed to its rapid spread, according to security vendor Bitdefender. The authors of the malware likely sold it as a service to different threat actors, too, contributing to its viral spread.

Over the course of 2021, threat actors used different SMS messages to try and trick users to click on the malicious link, including one that purported to be from a friend wanting to share a photo and another that tried to get users to listen to a fake voicemail message. Researchers from Bitdefender even observed attackers sending SMS phishing messages that ironically enough warned recipients about their devices being infected with FluBot and to take remedial action by clicking on the message link. In a report this January, Bitdefender identified Australia as the country most hit by FluBot, followed by Germany, Poland, Spain, and Austria.

Researchers from Proofpoint who tracked FluBot last year reported observing FluBot SMS messages in both English and German. The vendor said it had identified more than 700 unique domains that FluBot actors used for the English-language campaign alone.

Android Threats Continue to Surge

The FluBot takedown eliminates — temporarily — one of the biggest threats to Android device users in recent years. However, numerous other similar malware tools in the wild continue to present a serious threat. A recent report from ThreatFabric identified a continued increase in Android malware families such as Joker that enable fraudulent transactions being initiated from an infected device. Other examples include Alien, Cerberus, Hydra, and Octo.

The increase in Android malware families has also been accompanied by an increase in the number of malware droppers disguised as legitimate apps on Google's official Play mobile app store, ThreatFabric said. Among them is an app called NanoCleaner, which has been downloaded more than 10,000 times. In actuality, NanoCleaner is a dropper for Hydra.

Similarly, another app called Pocket Screencaster, with more than 10,000 installs, is a dropper for Octo, and another called Fast Cleaner, with more than 50,000 installs, is really a dropper for Alien and Octo.

"Threat actors continue to consider droppers on Google Play as one of the most effective ways to deliver malware to victims," ThreatFabric said.

About the Author(s)

Jai Vijayan, Contributing Writer

Jai Vijayan is a seasoned technology reporter with over 20 years of experience in IT trade journalism. He was most recently a Senior Editor at Computerworld, where he covered information security and data privacy issues for the publication. Over the course of his 20-year career at Computerworld, Jai also covered a variety of other technology topics, including big data, Hadoop, Internet of Things, e-voting, and data analytics. Prior to Computerworld, Jai covered technology issues for The Economic Times in Bangalore, India. Jai has a Master's degree in Statistics and lives in Naperville, Ill.

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