Gaining illegal entry to a secure system by faking the sender's address is one of the reasons why spoofing should be prevented. Spoofing is a technique that involves impersonating someone or something else to deceive or manipulate the recipient or target. Spoofing can be applied to various communication channels, such as emails, websites, phone calls, IP addresses, or DNS servers. One of the common goals of spoofing is to gain unauthorized access to a secure system by faking the sender's address, such as an email address or an IP address. For example, an attacker may spoof an email address of a trusted person or organization and send a phishing email that contains a malicious link or attachment. If the recipient clicks on the link or opens the attachment, they may be redirected to a fake website that asks for their credentials or downloads malware onto their device. Alternatively, an attacker may spoof an IP address of a trusted source and send packets to a secure system that contains malicious code or commands. If the system accepts the packets as legitimate, it may execute the code or commands and compromise its security. Therefore, gaining illegal entry to a secure system by faking the sender's address is one of the reasons why spoofing should be prevented.
References:
* https://www.kaspersky.com/resource-center/definitions/spoofing
* https://www.cisa.gov/resources-tools/resources/business-case-security
* https://www.avast.com/c-spoofing