The Stack Smashing Protector (SSP) is a security feature used in computer programming to prevent buffer overflow attacks. It works by placing a special value, known as a "canary," just before the stack return pointer. If a buffer overflow occurs, this canary value is altered, allowing the program to detect the overflow before executing potentially harmful code. When a program with SSP is compiled, it adds checks to ensure the integrity of the stack. If the canary value is changed, the program will terminate instead of continuing to execute, thus protecting the system from exploits that could compromise its security.