What characterizes a breach of information security?

A breach of information security is primarily characterized by unauthorized access to sensitive data. This occurs when individuals or systems gain access to information that they do not have permission to view or manipulate. Such breaches can result from various factors including hacking, insider threats, or inadequate security measures, ultimately compromising the confidentiality, integrity, and availability of protected information.

The other options reflect responses or steps that may be taken in the aftermath of a breach or as part of a security strategy, but they do not define what constitutes a breach itself. Enhanced security reviews and increased data encryption are proactive measures aimed at preventing breaches, while improved public relations would be a response to mitigate the fallout from a breach. Therefore, only unauthorized access directly describes the fundamental nature of an information security breach.