When you set CellSecurity up, it asks you what kind of traffic you want to allow through, and then goes immediately to work, constantly checking for unauthorized visitors. With additional features like port cloaking and automatic intrusion detection, it not only hides you from hackers, but even blocks traffic that merely looks suspicious.
CellSecurity gives you full control over all outbound programs. As with incoming traffic, it monitors every outgoing Internet transmission, checking to see which program is sending it and whether you've authorized that program to connect to the Internet. If you haven't authorized it, CellSecurity won't allow the information to leave your computer.