By default DP4 TCP/IP networking programs use port 5000. If you are planning to run DP4 over the Internet, or will be running DP4 on Windows XP, you may wish to consider using a different port. Port 5000 is also used by certain Windows XP services, and conflicts can therefore arise that prevent correct operation, either of DP4, or of Windows XP itself. (See DP4 on Windows XP for details). Also, because of known vulnerabilities in these Windows XP services, hackers may try to gain access to a system using this port, and you may want to close it.
It is extremely unlikely that a hacker would be able to do any real damage using this port if it is opened for TCPMGR. However a particularly malicious hacker might succeed in sending a packet that caused TCPMGR to hang or crash. Using the 4.621 version of TCPMGR should protect against this potential problem. However, there are known "exploits" that a hacker could use to gain unauthorised access to a computer running Windows XP, unless it has had all Microsoft security patches applied, or the SSDP service is disabled.
You can make DP4 networking use a different port by using the -socket command tail as described in Command Line options for DP4 network programs.