What defines a passive attack compared to an active attack?

A passive attack is characterized by the act of monitoring or eavesdropping on data transmission without making any alterations to the data itself. This form of attack often aims to gather information, such as usernames, passwords, or other sensitive data, without the target being aware of it.

In contrast to active attacks, which involve direct interaction with the target that can lead to data modification, disruption, or destruction, passive attacks rely solely on observation. The absence of interference or disruption to the target's operations is a key distinction that defines this type of attack, making data monitoring without alteration a defining feature.

The other options highlight actions typical of active attacks, such as interfering with system operation, engaging directly with the target, or installing malicious software, which all involve manipulation or modification of the system and data.