What term describes unauthorized access to an information system?

The term that describes unauthorized access to an information system is "Intrusion." Intrusion occurs when an individual gains access to a system without permission, typically by exploiting vulnerabilities or weaknesses in security measures. This concept is fundamental to cybersecurity as it highlights the risk of unauthorized entities gaining access to sensitive information, which can lead to data breaches, system compromise, and a host of malicious activities.

In contrast, while terms like "violation," "attack," and "access" relate to breaches of security, they carry different connotations. A violation often refers to a breach of policy or law rather than merely unauthorized technical access. An attack is more aggressive and may involve using various methods to disrupt or damage a system beyond just accessing it. Lastly, access is a general term that does not imply unauthorized entry; it can mean legitimate entry following proper protocols. Thus, "Intrusion" specifically encapsulates the essence of unauthorized access, making it the most accurate choice.