The method an attacker uses to get access to the system

Common methods: email, SMS, phishing

embedded malware, e.g. javascript within an SVG image or within compressed zip file

vishing - voice phishing, calling

war dialing - looking for unpublished numbers

802.1x (port based network access control) is important for protecting wireless networks to prevent people from plugging a physical device into a machine on the network and gaining access (Hardware Addition Attack)