Which of the following would be a sign that a network is experiencing a flood attack?

A network experiencing a flood attack typically shows signs such as increased latency and delays. This occurs because a flood attack, which often involves overwhelming the network with excessive traffic, can consume bandwidth, slow down response times, and hinder normal network operations. The sheer volume of incoming malicious traffic can prevent legitimate users from accessing network resources, leading to noticeable performance issues, such as delayed data transmissions and prolonged loading times for web applications.

The other options pertain to different types of security issues or performance problems. Unusual login activity is more indicative of authentication attacks, such as brute force attempts. Data encryption failures may signal issues related to data integrity or configuration errors rather than a flood attack. Lastly, missing system updates often reflect a lack of patch management but do not directly identify a flood attack; they could indicate broader vulnerabilities within the network. Therefore, network latency and delays serve as clear and specific indicators of a flood attack in progress.