It is theoretically feasible to modify the source code of mobile phone applications through technical means to monitor user behavior, but this behavior involves complex legal, ethical, and technical challenges. The following is a detailed analysis of this problem： --- ###**Technical feasibility** 1. **Source code modification and function implantation** -If you have the source code of the application (such as a self-developed application), you can insert the code to record user actions (such as clicks, inputs, and page stay times) and send the data to a remote server. -For third-party applications, the code needs to be modified through decompilation (such as Android's APK decompilation tool), but integrity verification (such as signature verification) may be triggered, causing the application to fail to run. 2. **Monitoring range** -**Basic behaviors**: page jumps, button clicks, usage time, etc. -**Sensitive data**: Intrusive monitoring is required, such as keyboard input records, camera/microphone calls, location information, etc. Such operations usually require system-level permissions (such as Android's AccessibilityService or iOS's jailbreak environment). 3. **Technical barriers** -**Difficulty of decompiling**: Modern applications generally use code obfuscation (such as ProGuard, OLLVM) to prevent reverse engineering. -**System restrictions**: iOS devices that are not jailbroken cannot directly modify system applications, and Android systems with higher versions have strict restrictions on background services. -**Concealment**: Real-time monitoring needs to be resident in the background, and may be noticed by users due to abnormal power consumption and traffic. --- ###**Legal and ethical risks** 1. **Privacy legal constraints** -**International level**: The European Union's "General Data Protection Regulation" (General Data Protection Regulation), the United States "California Consumer Privacy Act" (CCPA), etc. require users to explicitly agree to data collection. -**Chinese regulations**: According to the "Personal Information Protection Law of the People's Republic of China", collecting personal information without the informed consent of users is an illegal act and can face a fine of up to 5% of turnover. 2. **App store policy** - Google Play and Apple App Store strictly prohibit the application of hidden monitoring functions. If you submit a revised application, it may be removed from the shelves for violating the privacy policy. 3. **Copyright and agreement issues** -Modifying the source code of a third-party application may violate the software license agreement and constitute infringement. --- ###**Actual scenarios and suggestions** 1. **Legal use case** -**Enterprise equipment management**: To monitor the equipment allocated by the company through the MDM (mobile device management) program, you need to inform the employees in advance and obtain their consent. -**Parental control**: Using legal monitoring software (such as Google Family Link, Apple screen usage time), it needs to be explicitly enabled on children's devices. 2. **Illegal risk** -If you install a monitoring program on another person's device without authorization, you may violate the “crime of illegally obtaining computer information system data” or “crime of infringing on citizens' personal information” in the Criminal Law. 3. **Protective measures** -Users should regularly check application permissions, installation sources, and use security software to detect abnormal behavior. -Developers can improve application security through code obfuscation, HTTPS communication, and anti-debugging mechanisms. --- ###**Conclusion** It is technically achievable, but monitoring without the user's consent is illegal and unethical. It is recommended to give priority to legal and transparent solutions and always comply with privacy protection regulations.