What is defined as an actual occurrence of an adverse event?

The term that describes an actual occurrence of an adverse event is "attack." In the context of cybersecurity, an attack refers to any unauthorized attempt to access, compromise, or disrupt a system's integrity, availability, or confidentiality. This can manifest as various forms such as malware incidents, phishing attempts, or denial-of-service attacks, among others. The fundamental characteristic of an attack is that it represents a real event where a system or network is targeted with the intent to exploit vulnerabilities, making it a concrete instance of an adverse event in the realm of cybersecurity.

The other terms listed do not encapsulate the concept of an actual event in the same way. An audit trail is a record that documents user activities and system changes, providing a historical account rather than an event; authenticity pertains to the validity or genuineness of information or communication and does not specify an occurrence; and a backdoor is a method of bypassing standard authentication, which can be utilized in attacks but is not itself an event. Understanding the specific meaning of these terms is crucial for effectively navigating cybersecurity concepts and responding to incidents.