What Does Passive Attack Mean?
A passive attack, in computing security, is an attack characterized by the attacker monitoring communication or systems. This can take forms such as reading emails, tracking internet use, or using a system's microphone and camera to "spy" on an individual. In a passive attack, the intruder/hacker does not attempt to alter the system or change data.
Techopedia Explains Passive Attack
Passive attacks basically mean that the attacker is eavesdropping. This is in comparison to an active attack, where the intruder attempts to break into the system to access or change data. Even though a passive attack sounds less harmful, the damage in the end can be just as severe if the right type of information is obtained.
While it is possible for passive attacks to be performed for non-malicious reasons, such as marketing research, they are often initiated in order to gather information that can then be used to launch a much more harmful active attack.