Mobile App Security: A Practical Guide for Business Owners

You don't need to be technical to hold your team to a good standard. Here is what matters and what to ask.

Why app security is different

A mobile app runs on a device you don't control. The user's phone might be lost, rooted, infected or running an old operating system. Anyone can download your app and take it apart to see how it talks to your servers.

The practical rule: never trust the app itself. Treat the phone as a hostile environment. All real security decisions must happen on your server.

The main risks

Security teams often use the OWASP Mobile Top 10, a widely used list of common mobile risks. In plain terms, the biggest ones are:

Key points

  • Insecure data storage. Passwords, tokens or personal data saved in plain text on the device.
  • Weak authentication. Easy passwords, no limits on login attempts, long-lived sessions.
  • Insecure communication. Data sent without proper encryption.
  • Weak server and API security. The back end trusts whatever the app sends.
  • Insecure third-party code. Libraries and SDKs with known flaws or too much access.
  • Poor privacy controls. Collecting more data than needed.
  • Hardcoded secrets. API keys or passwords embedded in the app code.
  • Insufficient testing. Security bugs shipped because nobody looked.

1. Collect and store less

The safest data is data you never hold.

If you must store something sensitive on the phone, use the platform's secure storage: the iOS Keychain and Android Keystore. Do not use plain files or basic preferences for secrets.

Key points

  • Ask whether you really need each piece of personal information
  • Avoid storing sensitive data on the device when the server can hold it
  • Delete data when it's no longer needed
  • Don't log personal data or tokens in app logs or analytics

2. Protect data in transit

Use HTTPS with modern TLS for all network traffic, with no exceptions for "testing". Consider certificate pinning for high-risk apps such as finance or health, understanding that it needs careful maintenance. Never send passwords or personal data in URLs. Don't rely on the app to enforce security rules. Enforce them on the server.

3. Build login and sessions properly

Use a proven authentication service or standard, rather than inventing your own. Support multi-factor authentication where the data is sensitive. Offer biometric unlock (Face ID, fingerprint) as a convenience on top of proper login, not a replacement. Use short-lived access tokens with refresh tokens, stored securely. Limit login attempts and watch for suspicious activity. Let users see and end active sessions. Make password reset secure and not easily abused. Log users out when appropriate, especially for sensitive apps

4. Lock down the server and APIs

Most serious incidents involve the back end.

Key points

  • Check permissions on every request. Make sure user A can never fetch user B's data by changing an ID.
  • Validate and clean all input on the server
  • Rate limit sensitive endpoints
  • Don't expose more data than the app needs in API responses
  • Keep servers, databases and dependencies patched
  • Separate test and live environments, with different keys
  • Back up data and test the restore
  • Use least privilege: each service gets only the access it needs

5. Keep secrets out of the app

Anything inside the app package can be extracted. That includes:

Keep these on the server. If the app needs to call a third-party service, route the call through your server, which holds the key.

Key points

  • API keys for paid services
  • Database credentials
  • Private signing keys
  • Admin endpoints

6. Control third-party code

Modern apps include many libraries and SDKs for analytics, ads, crash reports and payments.

Key points

  • Keep a list of every third-party component
  • Use well-maintained, widely used libraries
  • Update dependencies regularly and scan them for known vulnerabilities
  • Review what data each SDK collects and sends, since it becomes your responsibility
  • Remove anything you no longer use

7. Respect privacy and permissions

Ask for permissions at the moment they're needed, with a clear reason. Work gracefully if the user says no. Write an accurate privacy policy and store declarations. Honour data deletion and access requests. Follow laws that apply to your users, such as GDPR (the EU's data protection law) or children's privacy rules. Be careful with location, contacts, photos and health data

8. Protect the code and the build

Use code obfuscation for sensitive apps to make reverse engineering harder. It slows attackers down but isn't a substitute for good design.. Detect rooted or jailbroken devices if your risk level justifies it, and decide how the app should respond. Sign builds properly and protect signing keys. Restrict who can publish to the app stores. Use a build pipeline with access controls and logs. Turn off debug features and verbose logging in production

9. Test security before release

Costs vary. A focused independent test often costs a few thousand dollars for smaller apps, and more for complex ones. Treat it as insurance.

Key points

  • Automated scans of code and dependencies on every build
  • Manual code review of login, payments and data handling
  • Penetration testing by an independent specialist before launch for apps handling sensitive data, and again after major changes
  • Test on real devices including older operating systems
  • A bug reporting channel so researchers and users can tell you about issues

10. Prepare for incidents

Assume that something will eventually go wrong.

Many laws require you to notify users and authorities within a set time after a breach involving personal data. Know what applies to you.

Key points

  • Know who is responsible for security on your side and your developer's side
  • Monitor errors, unusual traffic and failed logins
  • Have a written plan: who investigates, who informs users, who contacts regulators
  • Be able to push an urgent fix and force an update for dangerous versions
  • Keep logs long enough to investigate, without storing sensitive data in them

Questions to ask your developer

Clear, specific answers are a good sign. Vague ones are a warning.

Key points

  • Where is sensitive data stored, on the phone and on the server?
  • How do you protect login and sessions?
  • How do you make sure one user can't see another user's data?
  • Are any secrets stored inside the app?
  • Which third-party SDKs do we use, and what do they collect?
  • How do you scan dependencies for vulnerabilities?
  • Will we get an independent security test before launch?
  • What happens if we need to push an emergency fix?
  • How do we handle data deletion requests?
  • Who monitors the system after launch?

Next step

Building an app that handles sensitive data? We'll walk through your risks, review your design and set a security plan before you build. Talk to DECHY.