TL;DR
Yes, a flash drive can infect your Android device and then potentially spread that infection to your Windows PC. However, it’s not automatic and requires specific actions from you. Modern Android is fairly secure by default, but older versions or those with USB debugging enabled are more vulnerable. Windows can be infected if the Android malware is designed to exploit vulnerabilities on connected PCs.
How an Infection Might Happen
- Android Infection: A malicious file (e.g., APK, document with a macro) is placed on the USB drive.
- User Action on Android: You plug the USB drive into your Android device and open/execute the malicious file. This could be through a file manager app or by accidentally opening it if auto-launch is enabled (rare these days).
- Malware Installation: The malware installs itself on your Android device. This might involve requesting permissions, disguising itself as a legitimate app, or exploiting vulnerabilities.
- Connecting to Windows: You connect the infected Android device to your Windows PC via USB. The connection mode is crucial (see Step 4).
- Windows Infection: If the malware on Android is designed to do so, it attempts to install itself onto your Windows PC. This could happen through:
- Exploiting vulnerabilities in Windows when the device appears as a storage device.
- Using autorun features (less common now but still possible).
- Social engineering – prompting you to run a file or install software on Windows.
Steps to Prevent Infection
- Scan USB Drives: Always scan any USB drive with an up-to-date antivirus program before opening files on any device, including your Android phone and your PC.
- On Windows: Right-click the drive in File Explorer and select ‘Scan for viruses’.
- On Android: Use a reputable mobile security app (e.g., Bitdefender Mobile Security, Norton Mobile Security) to scan the USB drive after connecting it.
- Be Careful What You Open: Avoid opening files from unknown or untrusted sources on both your Android and Windows devices.
- Pay close attention to file extensions (e.g., .exe, .apk, .scr).
- Be wary of documents asking you to enable macros.
- Disable Auto-Launch: Most Android versions don’t automatically launch files from USB drives anymore. However, check your file manager settings to ensure auto-launch is disabled.
- USB Connection Mode Matters: When connecting your Android device to Windows:
- File Transfer/MTP mode (default): This is the safest option as it presents the phone’s storage as a drive. Malware has limited access in this mode unless specifically designed to exploit MTP vulnerabilities.
- PTP Mode: Used for transferring photos, less risky than debugging but still be cautious.
- USB Debugging (Developer Options): Disable USB debugging unless you are actively using it for development purposes! This mode gives your PC much greater access to your Android device and significantly increases the risk of infection. To disable:
- Go to Settings > About Phone
- Tap ‘Build Number’ seven times to unlock Developer Options.
- Go to Settings > System (or similar) > Developer Options
- Toggle USB debugging OFF.
- Keep Software Updated: Regularly update your Android operating system and all apps, as well as your Windows operating system and antivirus software.
- Use a Reputable Antivirus: Install a reputable antivirus program on both your Android device and your Windows PC. Ensure it has real-time scanning enabled.
What to Do If You Suspect an Infection
- Disconnect Immediately: Disconnect the USB drive and the infected Android device from any computers or networks.
- Scan with Antivirus: Run a full system scan on both your Android device and Windows PC using up-to-date antivirus software.
- Factory Reset (Android): If you strongly suspect an infection on your Android device, consider performing a factory reset. Back up important data first! Settings > System > Reset options > Erase all data (factory reset).
- Windows Reinstall: In severe cases of Windows infection, reinstalling the operating system may be necessary.