NetMon is a very useful app that can identify which of your mobile apps contain open ports and help you measure whether your network allows the traffic to open ports. By using this app, you are contributing the open-port related data to our study, and must be at least 18 years old. Otherwise, please exit. We will in turn provide you the in-depth knowledge about open ports in applications installed on your phone. We intend to make this a long-term study. Once you agree to use NetMon, it will collect the open-port data automatically for you and display them to you. You can also manually trigger the open-port analysis through NetMon's user interfaces. After NetMon uploads the displayed open-port data to our secure server, we will analyze them for research purpose. As a participant, you will obtain: (1) the raw and statistical data on different apps' open ports; (2) the raw and statistical data on different networks' policy on the traffic to open ports. These results will eventually advance the scientific knowledge on open ports in mobile applications. There are no anticipated risks to the participants participating in this study. To guarantee your confidentiality and privacy, (1) we will only collect the information that is not individually identifiable including apps' open-port related data (those you can see on NetMon' UI) and basic hardware information (no IMEI, and ANDROID_ID is hashed with salt). (2) we will transmit the collected data to the industry-level secure server using the standard encryption method via HTTPS. (3) only the NetMon research team will have access to the collected raw data. More information is available in the app-side term-of-use dialog.