How do you detect if an app is stealing your data?

As the creator of a gallery-cleaning app known as Sponge, I often hear the question: "Does this app steal my data?" I could walk you through Sponge’s privacy policy a hundred times, but why should you take my word for it? Instead of just telling you to trust me, I want to equip you with the knowledge to assess any app’s behavior yourself.

This article isn’t just about Sponge—it’s about helping you spot red flags in any app that might be mishandling your data. By the end, you’ll have a clearer understanding of what to look for and how to protect your privacy.

While there’s no foolproof method to detect every privacy risk, understanding certain red flags can help you make informed decisions. This article will give you practical tips to spot potential data misuse and better protect your privacy.

What does "data" refer to?

In the context of apps, data includes personal information such as:

• Location

• Messages and contacts

• Phone calls and call logs

• Internet activity

• Camera and microphone access

• Clipboard data

• Files 

Apps can request access to these, sometimes for legitimate reasons—but if an app asks for data unrelated to its function, that’s a sign to be cautious.

What is data stealing?

When I say data stealing, I’m referring to any access, modification, sharing, or copying of your data without true consent. And by consent, I don’t just mean clicking an “I agree” button that hands over your data without real choice. True consent means an app should only use your data for the specific purpose you intended while using it.

For example, if a simple flashlight app requests access to your contacts—you should ask: Why does it need my contact list? If there’s no legitimate reason, that’s a red flag.

Why do apps steal data?

There can be various motives behind data theft, I am just highlighting two main ones.

Selling Data to Third Parties

• Some companies sell your information to data brokers, who then resell it to advertisers, political groups, or even unknown entities.

Identity Theft & Fraud (in extreme cases)

• Malicious apps can access personal details like messages, calls, or financial information to commit fraud or steal identities.

How to spot red flags in Apps?

🚩Flag Check #1: Is the app requesting permissions it doesn’t actually need?

Check for application permissions, if they are aligned with tasks that you like to perform with the app. For e.g. Gallery access permission is required for a photo editing app, but a simple calculator app asking for microphone access is a major warning sign. What possible purpose could it serve for a calculator to record audio? This might indicate an attempt to eavesdrop on conversations or collect voice data.

Here is how you can check app permissions.

For iOS:

Change app permissions
You can go to Settings > [App Name] to view and manage all permissions for a specific app.

Change permissions based on their type

Go to Settings  > Privacy & Security.
You'll see a list of different permission categories like "Location Services", "Contacts", "Photos", "Camera", "Microphone", and more. Tap on any. A list appears showing the apps that requested access. If you find any access irrelevant to the requesting app, you can then toggle the switch next to each app to revoke access to that specific permission.

For Android:

Change permissions by app

1. On your device, open the Settings app.

2. Tap Apps.

3. Tap the app you want to change. If you can't find it, tap See all apps. Then, choose your app.

4. Tap Permissions. If you have allowed or denied any permissions for the app, you’ll find them here.

5. To change a permission setting, tap it, then choose Allow or Don't allow.

Change by permissions type

You can check which apps have the same permission setting. For example, you can check which apps have permission to check your calendar.

1. On your device, open the Settings app.

2. Tap Security & Privacy > Privacy Control > Permission manager.

3. Tap a permission type. If you have allowed or denied permission to any apps, you’ll find them here.

4. To change an app’s permission, tap the app, then choose your permission settings.

Read more about types of permission from Google.

🚩 Flag Check #2: Review app network activity and data consumption

To spot if an app is uploading your data, monitor its data usage. Unusually high data consumption — especially if it's beyond the app’s expected function — could be a red flag that your media or information is being sent to external servers.

For iOS:

Go to Settings > Mobile Data (or Cellular) — scroll down to see a list of apps and how much mobile data each app has used.

Note: Unfortunately, iOS doesn’t show Wi-Fi data usage per app.

App Privacy Report

In iOS 15.2 and later, Apple introduced a feature called App Privacy Report that lets you check which domains your apps are interacting with. This means you can see which websites and servers the apps are contacting in the background, giving you more insight into your data privacy.

Here’s how to check it:

1. Go to Settings > Privacy > App Privacy Report.

2. Tap App Privacy Report to see detailed information about:

   • Which domains each app is communicating with.

   • How often apps access sensitive data like your location, photos, microphone, and camera.

   • Network activity, showing data transferred between apps and external servers.

This feature helps you monitor apps for any suspicious behavior, such as unexpected data sharing or connections to unknown domains, which could be a privacy concern.

You can use any domain lookup tool to learn more about the domain with which apps are communicating. I tried https://www.virustotal.com/gui/home/url , and found good information.

Others are: 

• Cisco Talos Intelligence https://talosintelligence.com/ 

• AbuseIPDB  https://www.abuseipdb.com/

For Android:

Go to Settings > Network & Internet or Connections (depending on your device) > Data Usage > Tap on it to see a list of apps and how much data each one has used.

Pro tip: Apps like GlassWire can monitor your real time network traffic also. 

Spot Hidden Activity: Extra Checks to Stay Safe

• 🔻Extra Check 1: Background activity
  If an app has storage access (media/files) + internet access + background data (Android) or background app refresh (iOS), it technically has the capability to upload your data in the background. Apps that aren't meant to upload media (like cloud backups or messaging apps) should show minimal data usage. Some data use is normal for things like analytics (often declared on Play Store or App Store), but unusually high data usage is a red flag.
  

• 🔻Extra Check 2: Keep an Eye on Battery Consumption
  Apps uploading data in the background will also drain your battery more than usual. Watch for unusual battery consumption patterns — especially in apps that shouldn't be heavily active. Both Android and iOS allow you to check battery usage by app to spot any suspicious activity.

Final Words

Remember, no app can steal your data without the right combination of permissions and sneaky behavior. While no method is 100% foolproof, staying aware of permissions, data usage, and background activity can protect you from most hidden risks.

I wrote this not just to defend my app, but to help you build a general habit of questioning app behavior — including mine. Trust is built with clarity, not claims. Stay curious, stay safe.

Feature Photo by cottonbro studio

Fellow builders, let’s make privacy-first apps the norm. Drop your thoughts!