Which of the following is a common indicator of a data breach?

Unexplained data loss is a strong indicator of a data breach because it often suggests that unauthorized individuals have accessed and removed or compromised sensitive information. In the context of cybersecurity, this could imply that an attacker has successfully infiltrated a system, leading to the exfiltration of data without the organization's knowledge. Detecting anomalies like unexpected data loss alerts security personnel to investigate potential breaches and take necessary mitigation actions.

In contrast, increased website traffic might be due to legitimate marketing efforts, system upgrades typically improve security and functionality rather than indicating a breach, and regular security updates are expected practices that help prevent breaches rather than signify their occurrence. Each of these other options does not directly point to a compromise in data security, making them less relevant to indicating an actual data breach situation.