A self-signed certificate is a certificate that is signed by its own private key rather than by a trusted certificate authority (CA). This means that the authenticity of the certificate relies solely on the issuer's own authority. If a spoofed identity was detected, it could indicate that a private key associated with a self-signed certificate was compromised. Self-signed certificates are often used internally within organizations, but they carry higher risks since they are not validated by a third-party CA, making them more susceptible to spoofing.
References = CompTIA Security+ SY0-701 study materials, particularly the domains discussing Public Key Infrastructure (PKI) and certificate management.