Most mobile users know to stick to official app stores to download software — and for good reason. Even though legitimate third-party stores exist, the average user can find everything they need on a first-party platform like the Google Play Store or Apple’s App Store. And while Android — unlike apple — does allow sideloading (downloading installation packages directly off the web) even for regular users, this is usually practiced by people who know what they’re doing and are familiar with the risks.

When publishing an app on the Play Store or App Store, a developer has to pass a robust set of vetting processes, both for themselves and their applications. This vetting process involves both automated and manual testing, making these platforms far safer than third-party app stores and other means of installing software. That being said, users are recommended not to blindly trust even these first-party platforms, as there have been several cases where malicious apps slipped through the cracks in the vetting process. And while both Google and Apple are quick to respond when they detect malicious apps on their stores, the very fact that these malicious apps make it onto these platforms is proof that even their strict vetting processes are not foolproof.

How Do These Apps Make It Onto These Platforms?

No verification system is ever completely airtight, especially when you’re dealing with something as complex as app store vetting. For a malicious actor who knows what they’re doing, slipping past automated checks isn’t particularly difficult. In a lot of cases, it boils down to satisfying a specific list of requirements.

The harder part is clearing a manual review, since that involves human judgment. But even that isn’t impossible. A common tactic is to first publish a legitimate, fully functional app for the specific purpose of passing inspection. Once it’s live and has built some credibility, the app quietly receives an update containing malicious code. This is known as versioning. In other cases, the initial version remains harmless but downloads and executes malicious payloads after installation, either after a specific amount of time or due to certain conditions (like account creation or granting certain permissions) being met. That’s what happened with the Anatsa trojan — a campaign that used innocent-looking document viewer apps to deliver banking malware. Once installed, these apps fetched encrypted malicious code from remote servers, giving attackers access to users’ financial data and even access to their accounts.

It also doesn’t help that human reviewers are under constant pressure. With thousands of apps being submitted daily, there’s only so much attention they can give to each one. And then there’s also the fact that verified developer accounts can be hijacked or sold, allowing attackers to publish apps under legitimate names. Not to mention the cases where malicious software which mimics legitimate and trusted apps also end up being published on these stores. Between automated systems, human fatigue, and social engineering, the cracks in the process are wide enough for malicious apps to slip through.

Knowledge Really Is Power

Just because an application has made it to a first-party app store doesn’t automatically make it a legitimate or safe-to-use app. Like we’ve already discussed, as rigorous as the vetting process is, it’s still possible for malicious apps to end up being published on these platforms. As with any cyberthreat, awareness and good judgment are your strongest defenses. Sticking to well-known apps and developers, keeping your software up to date, and reading reviews (not just on the store) are actions you can take to ensure you don’t end up falling victim to a trojan application that has snuck its way onto the Play Store or App Store.