Ports are used by software to connect to servers on the Internet. Open ports allow transmissions, while closed ports reject them. Firewalls can close ports to prevent malicious attacks. Port numbers identify each port and some are reserved for specific services. Open ports can be vulnerable to attacks from hackers and malware, making closed ports essential for security.
A port is a conduit to the Internet that computer software uses to contact its server. These ports refer to commonly known TCP/IP ports, named after Transmission Control Protocol and Internet Protocol. When a port is open, it means that the specific port is configured to allow transmissions between the software and its server and accept packets from external sources. A closed port is the opposite, it ignores and does not accept packets that may be transmitted to it.
Its inaccessibility isn’t the only defining feature of a closed door. A closed port is considered closed not only if it is unreachable, but also if there is no software listening on that port. Software listening on a port means that there is an application that can receive transmitted packets and recognize them. When no application is listening on a port, packets directed to that port are automatically rejected by the operating system of that computer.
Firewalls can be used to close ports. The user only needs to configure their firewall to allow specific packets through for certain ports, while other ports can be considered closed for all intents and purposes as no packets will be allowed. This way, unexpected packets that may or may not come from malicious sources will be ignored and dropped from any closed ports.
The numbers, called port numbers, identify each port. As a common practice, some port numbers are reserved for use by specific types of services. Unused port numbers are usually closed for security reasons.
Acting as a gateway between the software installed on the client computer and the server, ports can also act as paths for malicious attacks. Unscrupulous individuals can use the software to scan open ports in computers they detect on the Internet and to detect any applications listening on those open ports. When they find such an opening, they can exploit the open channel to get confidential data, sabotage the target computer, take control of it or other illicit activities.
Another vulnerability of open ports is the possibility that authentic services are misconfigured or that downloaded software is anything but benign. Malware masquerading as useful software can act as a service, listening on a port for hackers to gain access to the target computer. Thus, hackers do not have to search for such unprotected computers and can rely on malware to lead them to such openings. A closed port is therefore the key to defeating such attacks, whether from malicious software inside the computer or from attackers from remote connections.
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