Digital certificates are electronic documents that use public key cryptography to verify the identity and authenticity of the sender and the receiver of encrypted communications. Digital certificates are issued and signed by trusted entities called certificate authorities (CAs), and they contain information such as the public key, the name, and the expiration date of the certificate. Digital certificates enable network security devices to decrypt perimeter traffic and inspect it for command and control communications or other malicious activity. References := Understanding Cisco Cybersecurity Operations Fundamentals (CBROPS) - Cisco, page 51.

A certificate authority (CA) is a trusted entity that issues and manages digital certificates for secure communication over the internet. A digital certificate is a document that contains the public key and the identity of the owner of the key. A CA impacts security by validating the domain identity of the SSL certificate, which is a type of digital certificate that enables encrypted communication between a web server and a web browser. The CA verifies that the domain name in the certificate matches the domain name of the web server, and signs the certificate with its own private key. The web browser can then verify the signature of the CA and trust the identity of the web server. References := Cisco Cybersecurity Operations Fundamentals, Module 2: Security Monitoring, Lesson 2.3: Cryptography and PKI, Topic 2.3.2: Public Key InfrastructureReference: https://en.wikipedia.org/wiki/Certificate_authority

The containment phase of the incident response lifecycle is focused on limiting the impact of an active incident and preventing it from continuing or spreading further. In this scenario, the organization is experiencing a suspected Distributed Denial-of-Service (DDoS) attack, as indicated by high-volume traffic and degraded application performance.
During containment, the Computer Security Incident Response Team (CSIRT) takes immediate actions such as rate limiting, blocking malicious IP addresses, diverting traffic through scrubbing services, or engaging DDoS mitigation providers. The goal is to stabilize services and ensure that the attack no longer affects business operations. This phase also includes confirming that defensive measures have been successfully applied.
Preparation occurs before an incident and involves planning and readiness activities. Eradication focuses on removing the root cause of the incident, such as disabling attacker infrastructure or removing malware, which is not applicable to most DDoS scenarios. Recovery occurs after containment and involves restoring systems to normal operation and monitoring for recurrence.
Cybersecurity operations documentation clearly defines containment as the phase where ongoing attacks are stopped or controlled. Therefore, containment is the correct answer.

The event described falls under the 'action on objectives' category of the Cyber Kill Chain. This stage occurs after the attacker has established a foothold within the network and begins to execute their intended actions, such as data exfiltration. References: The Cyber Kill Chain framework outlines the stages of a cyberattack, with 'action on objectives' being the final step where attackers achieve their primary goal, such as data theft