The defensive technologies that are being employed by the system are an obvious source of information. These technologies include physical security, but will effectively inform the attacker about which risks they face when conducting their attack. For example, if NetFlow is being used, they may need to consider masking their own IP addresses and hence location. If a certain antivirus is being used, they may want to pre-scan their tools to see if it will get through.

Imagine someone attempting to attack a building. If they know that there are metal detectors being used, they know that certain attacks are unlikely to work.