A PDF creator app potentially served a Trojan to more than 100 million Android users via downloads on the Google Play store.

In summer 2019, the CamScanner – Phone PDF Creator app caught the attention of Kaspersky Lab. The program had generated more than 100 million downloads through the Google Play store, but in July and August, it began to receive negative user reviews suggesting the presence of unwanted features.

Upon a closer look, security researchers discovered that the app used an advertising library that contained a malicious dropper at the time of analysis. This dropper, detected by Kaspersky as Trojan-Dropper.AndroidOS.Necro.n, decrypted and executed malicious code contained within the mutter.zip file in the app’s resources. The dropper then decrypted a configuration file, revealing several locations from which it could download and then execute an additional module as its malicious payload.

After Kaspersky reported its findings to Google, the app was promptly removed from the app marketplace.

Malware Hiding on the Google Play Store

Trojan-Dropper.AndroidOS.Necro.n isn’t the only malware family that’s been found on the Google Play store. In April 2019, for instance, Check Point detected a clicker malware family, dubbed PreAMo, that generated more than 90 million downloads across six apps available on the Play store.

That was just two months before ESET discovered several apps available for download on Google’s official app marketplace that were capable of stealing one-time passwords in SMS-based two-factor authentication (2FA) messages without achieving the proper permissions. And in August 2019, Trend Micro detected adware hidden within 85 photography and gaming apps that had registered a combined total of 8 million downloads on the Google Play store.

How to Defend Against Mobile App Threats

Security professionals can help defend their organizations against threats like Necro.n by following mobile security best practices, which include keeping devices up to date with the latest software patches and restricting app downloads to only trusted developers on official app marketplaces. Companies should also use a unified endpoint management (UEM) tool to monitor all devices for suspicious activity and automatically remediate suspicious behavior.

More from

2022 Industry Threat Recap: Finance and Insurance

The finance and insurance sector proved a top target for cybersecurity threats in 2022. The IBM Security X-Force Threat Intelligence Index 2023 found this sector ranked as the second most attacked, with 18.9% of X-Force incident response cases. If, as Shakespeare tells us, past is prologue, this sector will likely remain a target in 2023. Finance and insurance ranked as the most attacked sector from 2016 to 2020, with the manufacturing sector the most attacked in 2021 and 2022. What…

X-Force Prevents Zero Day from Going Anywhere

This blog was made possible through contributions from Fred Chidsey and Joseph Lozowski. The X-Force Vulnerability and Exploit Database shows that the number of zero days being released each year is on the rise, but X-Force has observed that only a few of these zero days are rapidly adopted by cyber criminals each year. While every zero day is important and organizations should still devote efforts to patching zero days once a patch is released, there are characteristics of certain…

And Stay Out! Blocking Backdoor Break-Ins

Backdoor access was the most common threat vector in 2022. According to the 2023 IBM Security X-Force Threat Intelligence Index, 21% of incidents saw the use of backdoors, outpacing perennial compromise favorite ransomware, which came in at just 17%. The good news? In 67% of backdoor attacks, defenders were able to disrupt attacker efforts and lock digital doorways before ransomware payloads were deployed. The not-so-great news? With backdoor access now available at a bargain price on the dark web, businesses…

Hack-for-Hire Groups May Be the New Face of Cybercrime

Google’s Threat Analysis Group (TAG) recently released a report about growing hack-for-hire activity. In contrast to Malware-as-a-Service (MaaS), hack-for-hire firms conduct sophisticated, hands-on attacks. They target a wide range of users and exploit known security flaws when executing their campaigns. “We have seen hack-for-hire groups target human rights and political activists, journalists and other high-risk users around the world, putting their privacy, safety and security at risk,” Google TAG says. “They also conduct corporate espionage, handily obscuring their clients’ role.”…