Port

A port is basically a connection address specified to allow programs on different computers to communicate. This connection address is represented by a port number from 0 to 65536. Like legitimate programs, malware programs that connect to remote systems often use predefined ports. Some malware use random ports that are defined upon connection. System administrators and desktop users can increase system security by controlling the availability of certain ports.

Many ports used by malware and legitimate applications are assigned to specific protocols like HTTP, which uses port 80 by default. IANA maintains a list of port numbers and known uses.