What is an open port, how can it help detecting fraud?

Many ports have a well-defined set of services that use them and a port scan can reveal all ports that are available or we could say open. Therefore reading the open ports can give information on which software or applications are used with the IP address.

For example, should an application known for running on open port 1234 and scanning finds that the port is open for the user then we can state with reasonable confidence that the user also uses the said application.

Evidently, collecting all open ports that are known for suspicious or malicious activity is a great tool in fighting fraud.