The whole truth is, so much junk is being pushed with exaggerated claims, that unless you know otherwise I would stick with one of the tools I've reviewed and recommended on the next page. But if you're already using one of the many Evil Port Monitors, you should at least understand how it's compromising your security rather than enhancing it. When your computer is scanned by the typical Internet port scanner, connection attempts are made across a range of potential connection ports on your system. Some scanners target specific ports. Entry points to give intruders a foothold.
Entry points whose mere existence provides intruders with valuable information.
The wily cracker knows that the ports which accept connections imply the existence of server software that's listening and waiting to communicate. That's a place to mount an attack. They deliberately open connection ports that weren't open before and wait for passing scanners to test those connection points. The problem is that when they sense an intruder through a port, that intruder achieves a successful connection to your machine and is led to believe that a complex and probably insecure server is available to be compromised. When viewed from across the Internet, computers running Evil Port Monitors give the appearance of being the Grand Central Station of servers with a wide array of exploitable resources.