How Malicious Apps Secretly Steal Your Data (and How to Stop Them)
Malicious apps can steal your photos, passwords, and bank details silently. Learn how they work, how to spot them, and how to protect your phone right now.
5/22/202611 min read
How Malicious Apps Secretly Steal Your Data (and How to Stop Them)
Category: Mobile Security | Reading Time: 11 minutes
IN THIS ARTICLE
1. What malicious apps actually are
2. How they get onto your phone in the first place
3. The six ways they steal your data silently
4. Warning signs your phone may have a malicious app
5. How to check and remove suspicious apps
6. How to protect yourself going forward
7. Frequently asked questions
You downloaded what looked like a useful app. It worked exactly as advertised. You gave it a few permissions, forgot about it, and moved on with your day.
What you did not know is that the app was also quietly recording your microphone, reading your messages, logging every password you typed, and sending all of it to a server halfway across the world.
This is not a Hollywood plot. According to the Google Security Blog, Google blocked over 2.28 million policy-violating apps from being published on the official app store in a single year — and that is only the ones that were caught before reaching users.
https://security.googleblog.com/2022/04/how-we-fought-bad-apps-and-developers.html
Malicious apps are one of the most widespread and least understood threats to ordinary smartphone users. This guide explains exactly how they work, how they end up on your phone, and what you can do to protect yourself.
What Malicious Apps Actually Are
A malicious app is any application designed — either entirely or in part — to harm the person using it. The harm can take many forms: stealing data, spying on activity, draining bank accounts, displaying fraudulent advertisements, or giving a criminal remote access to your device.
What makes malicious apps particularly dangerous is that they are designed to appear completely normal. Many function exactly as advertised — a game, a torch, a calculator, a free VPN — while simultaneously performing harmful operations in the background without the user's knowledge.
The UK's National Cyber Security Centre (NCSC) has published guidance warning that malicious apps frequently disguise themselves as legitimate software, using familiar-looking icons and names to gain user trust before exploiting the permissions they are granted.
The US Cybersecurity and Infrastructure Security Agency (CISA) echoes this warning, noting in its Mobile Communications Best Practice Guidance that malicious apps often impersonate popular, trusted applications in order to deceive users into installing them.
There are several categories of malicious apps, each with a different primary method of attack:
Spyware — Apps that silently monitor your activity, recording keystrokes, capturing screenshots, accessing your camera and microphone, and transmitting the collected data to a remote server.
Trojans — Apps that appear entirely legitimate but contain hidden malicious code that activates after installation. The name comes from the ancient story of the Trojan horse — a gift that concealed an attack.
Adware — Apps that bombard your device with intrusive advertisements, sometimes clicking on ads automatically without your knowledge to generate fraudulent revenue for the developer.
Banking trojans — A specific category of trojan designed to steal financial credentials by overlaying fake login screens on top of genuine banking apps. When you think you are logging into your real bank app, you are actually handing your credentials to an attacker.
Stalkerware — Apps designed to secretly monitor a person's location, messages, and calls, typically used in cases of surveillance without consent.
How They Get Onto Your Phone in the First Place
Understanding how malicious apps reach your device is the first step to preventing it.
Through Third-Party App Stores
The official app stores — maintained by major platform providers — have review processes designed to detect malicious apps before they reach users. Third-party app stores, by contrast, often have no such review process at all.
The NCSC specifically warns against downloading apps from sources other than official app stores, noting that apps downloaded from unofficial sources carry a significantly higher risk of containing malicious code.
Through Official Stores — Occasionally
Even official app stores are not completely immune. The Google Security Blog reported that in 2021 alone, Google blocked 1.2 million policy-violating apps from being published — but some malicious apps do still make it through, particularly those that hide their malicious behaviour until after installation and approval.
https://security.googleblog.com/2022/04/how-we-fought-bad-apps-and-developers.html
Through Phishing Links
Cybercriminals send messages — by text, email, or through messaging apps — containing links that, when tapped, begin downloading a malicious app directly. The message often impersonates a trusted brand or organisation to make the download seem legitimate.
CISA has specifically warned that attackers use phishing links, fake update notifications, and cloned app pages that push malicious files onto devices, all while appearing to come from sources the user already trusts.
Through Fake Updates
A message or notification appears telling you that a popular app on your phone needs an urgent update. The update link takes you outside the official store. What you download is not an update — it is a malicious app using the original app's name and icon.
Through Repacked Legitimate Apps
Cybercriminals take a popular, legitimate app, add malicious code to it, and redistribute it. The repacked app looks and works exactly like the real one — but it also runs malicious processes in the background. This technique, known as trojanising, was documented by the NCSC in its advisory on the MOONSHINE and BADBAZAAR spyware variants, which hid malicious functions inside otherwise working legitimate apps.
The Six Ways Malicious Apps Steal Your Data Silently
Once installed, a malicious app can use several techniques to harvest your personal information — all without displaying any obvious sign of what it is doing.
1. Abusing App Permissions
When you install an app, it requests permissions — access to your camera, microphone, contacts, location, messages, and storage. Granting these permissions is necessary for many legitimate apps. But malicious apps request far more permissions than they need for their stated purpose, and then use those permissions to harvest your data continuously.
CISA's Mobile Communications Best Practice Guidance specifically advises users to review app permissions carefully, warning against granting access to sensitive permissions — including location, camera, and microphone — unless they are genuinely required for the app's core function.
A torch app that requests access to your contacts and microphone is a warning sign. A weather app that wants access to your messages has no legitimate reason for that permission.
2. Keylogging
Keylogging is the practice of recording every key pressed on your device — silently capturing passwords, messages, search terms, and any other text you type. A keylogging app runs invisibly in the background, collecting this data and transmitting it periodically to the attacker.
The cybersecurity research firm Kaspersky has documented numerous keylogging trojans targeting mobile devices, noting that they are particularly dangerous because they can capture login credentials for banking, email, and social media accounts without triggering any visible alert.
https://www.kaspersky.com/resource-center/threats/what-is-keylogger
3. Screen Capture and Screen Overlay
Some malicious apps take periodic silent screenshots of your device, capturing whatever is currently displayed — including open messages, banking screens, and login pages. Others use a technique called screen overlay, where a transparent fake screen is placed on top of a genuine app. When you think you are interacting with your real banking app, you are actually entering credentials into the attacker's invisible overlay.
4. Accessing Your Camera and Microphone
With camera and microphone permissions granted, a malicious app can silently activate either at any time — recording audio from your surroundings, taking photos or video, or listening to phone calls. The NCSC documented the MOONSHINE and BADBAZAAR spyware variants doing exactly this — once installed, they were observed accessing microphones, cameras, messages, photos, and location data without the user being aware.
5. Reading and Intercepting Messages
Malicious apps with access to your messages — including SMS, which is used to deliver one-time passwords for two-factor authentication — can intercept these codes and forward them to an attacker. This allows the attacker to bypass two-factor authentication on your accounts entirely, as they receive the verification code before you do.
6. Transmitting Data to Remote Servers
All of the data collected through the methods above is periodically packaged and sent to a remote server controlled by the attacker — a process that typically happens when your phone is connected to Wi-Fi to avoid detection through unusual data usage. The AV-TEST Institute, a leading independent cybersecurity testing organisation, registers over 450,000 new malicious programs and potentially unwanted applications every single day across all platforms.
https://www.av-test.org/en/statistics/malware/
IMPORTANT: All of these processes are designed to be completely invisible during normal use. Your phone continues to function normally, the app continues to do what it advertises, and nothing appears wrong. The theft happens entirely in the background.
Warning Signs Your Phone May Have a Malicious App
While malicious apps are designed to be invisible, they do leave behind indirect signs. Watch for these warning signals:
Battery draining faster than usual — Malicious apps running constant background processes consume battery power continuously. If your battery has started depleting significantly faster without any change in your own usage, it is worth investigating.
Unexplained increase in data usage — Malicious apps transmit stolen data to remote servers. If your mobile data usage has increased noticeably, go to your phone settings and check which apps are consuming data in the background.
Phone running hot when not in use — Sustained background processing generates heat. A phone that regularly feels warm even when sitting idle is a sign that something is running in the background.
New apps you do not remember installing — Check your full app list periodically. Some malicious apps install additional apps silently after gaining sufficient permissions.
Unusual account activity — Unexpected logins, password reset emails you did not request, or unfamiliar transactions can indicate that credentials harvested by a malicious app have been used by an attacker.
Ads appearing outside of apps — If you are seeing advertisements on your home screen or in places where ads have no business appearing, adware is likely running on your device.
Phone behaving strangely — Unexpected restarts, apps opening on their own, settings changing without your input, or unusual screen activity can all indicate malicious software running with elevated permissions.
How to Check and Remove Suspicious Apps
Review Your Installed Apps
Go through every app installed on your device and ask yourself: do I remember installing this? Do I actually use it? Does it have a legitimate reason to be on my phone? Remove anything you do not recognise or use.
On Android: Go to Settings, then Apps or Application Manager, and review the full list.
On iPhone: Go to Settings, scroll down to see all installed apps, and review the list.
Check App Permissions
Review what permissions each app on your device has been granted. Revoke any permissions that seem excessive for the app's purpose.
On Android: Go to Settings, then Privacy, then Permission Manager.
On iPhone: Go to Settings, then Privacy and Security.
Look specifically for apps that have access to your microphone, camera, location, contacts, or messages that have no obvious reason to need these.
Run a Security Scan
Use a reputable mobile security application to scan your device for known malicious software. The cybersecurity firms Kaspersky, Norton, and Bitdefender all offer mobile security tools that can detect and remove known malicious apps.
Update Your Operating System
Malicious apps frequently exploit known vulnerabilities in older operating system versions. Keeping your phone's software updated closes these vulnerabilities. CISA specifically recommends enabling automatic updates as a baseline protection measure against malicious app exploits.
Factory Reset as a Last Resort
If you have strong reason to believe your phone has been deeply compromised by malicious software, a factory reset — following the proper backup steps described in a previous article — will remove all installed apps, including malicious ones, and return the device to its original state.
How to Protect Yourself Going Forward
Prevention is significantly easier than detection or removal. These habits will dramatically reduce your risk of ever installing a malicious app.
Only download apps from official stores — The major platform providers operate review processes that, while imperfect, significantly reduce the risk of malicious apps compared to unofficial sources. The NCSC, CISA, and FTC all specifically recommend this as a primary protection measure.
Read reviews before installing — Look at the number of downloads, the age of the app, the developer's other apps, and the content of reviews. A newly published app with very few reviews asking for extensive permissions is a warning sign.
Question every permission request — Before granting any permission, ask whether this app genuinely needs this access to function. A permission request that does not make sense for the app's purpose is a red flag.
Keep your operating system updated — Updates frequently include patches for security vulnerabilities that malicious apps exploit. The FTC recommends enabling automatic updates on all devices.
https://consumer.ftc.gov/articles/how-recognize-and-avoid-phishing-scams
Be cautious with links that lead to app downloads — Never install an app through a link sent to you in a message, regardless of who it appears to come from. Always search for the app independently in the official store and download it from there.
Review your app list regularly — Make it a monthly habit to go through your installed apps and remove anything you do not use or recognise. The fewer apps on your device, the smaller your attack surface.
Enable Play Protect on Android — Google Play Protect scans all apps on your device continuously for harmful behaviour. Confirm it is enabled by going to the Play Store, tapping your profile icon, and selecting Play Protect.
https://security.googleblog.com/2022/04/how-we-fought-bad-apps-and-developers.html
Frequently Asked Questions
Can iPhones get malicious apps too?
Yes, although iPhones have historically faced a lower risk than Android devices due to the stricter review process of their official app store and the closed nature of the operating system. However, the NCSC has documented cases of malicious apps reaching Apple's official store, and devices where the operating system has been modified to remove built-in security restrictions face significantly higher risk. The CISA guidance on mobile security applies to both Android and iPhone users.
Do malicious apps only come from unofficial app stores?
No. While unofficial app stores carry a much higher risk, malicious apps have been found in official stores as well. Google reported blocking 1.2 million policy-violating apps in 2021 alone — which means some apps with harmful intent do make it through the review process before being identified and removed.
https://security.googleblog.com/2022/04/how-we-fought-bad-apps-and-developers.html
How can an app steal my data if I gave it permission?
When you grant an app a permission — such as access to your contacts or microphone — you are authorising it to use that feature. A malicious app uses those permissions for purposes beyond what it disclosed. You agreed to let the torch app use your camera for the torch function. You did not agree to let it photograph your screen and send the images to a remote server — but with camera permission granted, it has the technical ability to do exactly that. This is why reviewing what permissions each app actually needs is so important.
Is a slow phone always a sign of a malicious app?
Not necessarily. Phones naturally slow down over time as their hardware ages relative to increasingly demanding software. However, a sudden and unexplained change in performance — particularly combined with increased battery drain or data usage — is worth investigating. Check your running processes and recently installed apps first.
Can a malicious app steal my banking information?
Yes. Banking trojans are specifically designed to steal financial credentials. They do this either by overlaying a fake login screen on top of your genuine banking app, by keylogging the credentials you type, or by intercepting the one-time SMS codes used for two-factor authentication. Kaspersky has documented numerous mobile banking trojans active on Android devices that use these techniques.
https://www.kaspersky.com/resource-center/threats/what-is-keylogger
What should I do if I think a malicious app has already stolen my data?
Act immediately. Change the passwords to your email and banking accounts from a different, secure device. Enable two-factor authentication on all important accounts if not already active. Contact your bank to flag potential fraud. Run a security scan on your device. If you believe financial data was compromised, contact your bank's fraud team directly. Report the app to the official store where you downloaded it.
Are free apps more likely to be malicious than paid ones?
Free apps are more commonly exploited for malicious purposes, but paid apps are not inherently safe. The more reliable indicator is the developer's reputation, the number of verified downloads, the age of the app, and whether the permissions it requests match its stated functionality. Price alone is not a reliable indicator of safety.
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The Bottom Line
Malicious apps are designed to be invisible. They look like the real thing, they work like the real thing, and they give nothing away while they silently harvest your passwords, messages, banking credentials, photos, and location data in the background.
As the NCSC, CISA, and Google's own security team have all made clear, the threat from malicious apps is real, documented, and growing. But it is also highly preventable with a small number of consistent habits — downloading only from official stores, reviewing permissions carefully, keeping your software updated, and checking your app list regularly.
Your phone holds more personal information about you than any other object you own. The apps you install on it deserve the same level of scrutiny you would give to someone asking for your house keys.
Share this article with someone who downloads a lot of apps. One informed decision could be the difference between staying safe and handing a stranger the keys to your digital life.