Final answer:
Three computer ports that shouldn't be open by default due to security risks include Telnet (port 23), FTP (port 21), and RDP (port 3389). These ports are vulnerable to eavesdropping or unauthorized access if traffic is not encrypted and properly secured.
Step-by-step explanation:
On a computer, several ports should not be open by default because they could leave the system vulnerable to security breaches if not properly managed. Three such ports are:
- Telnet (port 23): This is an older protocol for remote command line administration that sends data in clear text. It is considered insecure because it is susceptible to eavesdropping.
- FTP (port 21): File Transfer Protocol is used for transferring files, but like Telnet, it does not encrypt its traffic. This can lead to data breaches if sensitive information is intercepted.
- Remote Desktop Protocol (RDP) (port 3389): Although useful for remote administration, an open RDP port can be exploited for unauthorized access and various attacks if not properly secured.
All of these ports can be used legitimately but can pose a significant security risk if they are open and exposed to the internet without proper security measures like authentication and encryption. It's generally best practice to keep these ports closed unless they are needed and adequately protected.