Calif. Shields Up probes benignly to tell how exposed your system might be. Enterprise firewalls do not automatically guarantee safety. Of the 65,535 packet ports available on every computer, one just might be open for something to sneak in. Shields Up can tell you whether a PC has any exposed ports and whether they are invisible in the state known as stealth mode. The three tested firewall applications close all the common ports, preventing most unauthorized access.
Many ports end up in stealth mode.
Behind an enterprise firewall or a proxy server, most ports remain closed but visible. A resourceful hacker can see them and sneak in. The Gibson Research probe examines the PC s most common entry ports, such as those used for File Transfer Protocol, Simple Mail Transfer Protocol, Telnet and other common Internet traffic. Visible ports are not the only concern, however. A user generally can t mask the system s IP address the string of numbers such as 123.12.456.78 that identifies it on the Internet.