In the context of network security, which action is categorized as eavesdropping?

In the realm of network security, eavesdropping specifically refers to the act of secretly listening to or monitoring communications over a network without the consent of the parties involved. The action of collecting network data without permission directly aligns with this definition, as it involves intercepting data packets or communication streams to gather information surreptitiously. Eavesdropping can occur through various methods, such as using network sniffers to capture data transmitted over unsecured connections, hence violating the privacy and confidentiality of the data being exchanged.

The other choices describe different malicious activities that do not fall under the traditional definition of eavesdropping. For instance, blocking access to a network involves preventing users from connecting, and attaching a malicious device focuses on physical security breaches that may facilitate further attacks. Disrupting access to legitimate users highlights a denial-of-service aspect, which is distinct from simply monitoring communications. Therefore, the appropriate choice accurately reflects the nature of unauthorized data collection in network communications.