Malicious optimizer, booster, and utility applications hosted on Google Play gathered nearly half a million downloads before being taken down, Trend Micro reports.
The apps, which are detected by the company’s products as AndroidOS_BadBooster.HRX, were designed to perform activities such as ad fraud, and to download around 3,000 malware variants or other malicious payloads to the infected devices.
Active since 2017, the campaign involved 9 malicious applications, with a collective download count of more than 470,000. Four of the apps gathered more than 100,000 downloads each before Google removed them from the official storefront.
All of the offending apps — they were named Shoot Clean, Super Clean Lite, Super Clean, Quick Games, Rocket Cleaner, Rocket Cleaner Lite, Speed Clean, LinkWorldVPN, and H5 gamebox — have been removed from Google Play.
The malware variants these apps drop onto devices masquerade as system applications and do not show icons on the launcher or application list.
Speed Clean, for example, was designed to launch a transparent activity background that hides malicious content from the user, while a service establishes a connection with remote ad configuration servers and registers the installation. Next, the app starts displaying malicious ad content.
The app can also download malware variants or other payloads on the infected device to perform additional ad fraud techniques, including simulating a user clicking on ads for malicious Google Play application. These apps are integrated in legitimate advertising platforms, such as Google AdMob and Facebook Audience Network.
The malicious payloads can also install rewarded apps from mobile advertising platforms — in a virtual environment, to prevent user detection — and can trick users into enabling accessibility permissions and deactivating Google Play Protect.
The apps can then abuse the affected device’s accessibility function to post fake reviews or to log in the new applications with users’ Google and Facebook accounts.
In 2017, when the campaign started, there were 6 malware variants these applications could download. Over 169 such malicious payloads were observed throughout 2018, roughly 2,600 emerged in 2019, and 33 more were added to the list at the beginning of 2020.
Over the past three months, Trend Micro observed more than 65,000 infections associated with the campaign. Japan was affected the most, with over 48,000 infections, followed by Taiwan with more than 5,700, the United States with nearly 2,500, Israel with over 1,950, and India with a bit more than 1,080.
Trend Micro’s security researchers observed that malicious content was being delivered to users regardless of the geographic parameter value of the country code, except for China, suggesting that the campaign’s operators attempt to avoid infecting users from this country.
“Fraudsters attempt to deceive users by making malicious apps look genuine, so users should do their due diligence before downloading any mobile app. Verifying an app’s legitimacy is typically done by checking user-created reviews on the Play Store. However, in this particular case, the malicious app is capable of downloading payloads that can post fake reviews unbeknownst to the user,” Trend Micro concludes.