Military and intelligence
In a military and intelligence context, reconnaissance involves dissimilar concepts, either conducting potential combat operations, or the gathering of information by physical observation or remote viewing with technological sensors.
- Armed reconnaissance: While it can apply to reconnaissance in force by ground or naval units, this usually refers to aircraft that overfly an area, not knowing where specific targets may be found but expecting to find and attack targets of opportunity.
- Reconnaissance in force: A military movement probing for enemy troops at unknown locations, reporting on their position when they are found, but immediately engaging them in full-intensity combat.
- Special reconnaissance: Also known as SR, missions deep in denied areas, conducted by special operations personnel. They may be in or out of uniform. While SR units may direct air, missile, or artillery strikes, they strive to stay undetected.
Reconnaissance satellites and reconnaissance aircraft also gather information. Without further detail, they are assumed to be primarily collecting imagery intelligence.
Computer network security
Network reconnaissance is a term for testing for potential vulnerabilities in a computer network. This may be a legitimate activity by the network owner/operator, seeking to protect it or to enforce its acceptable use policy. It also may be a precursor to external attacks on the network.
Certain apparent reconnaissance activities, which would be highly suspicious if coming from outside the network, may be perfectly normal network performance and reliability monitoring when performed inside the boundaries of the network. Some network intrusion detection systems have difficulty in determining if a reconnaissance activity is internal or external, and generate many false alarms causing fear, uncertainty and doubt.