What is the difference between agent-based scanning, and authenticated and unauthenticated scanning?

Agent-based scanning is a type of vulnerability scanning that uses a program installed locally on a host to increase visibility into the host and identify vulnerabilities, misconfigurations, and missing patches. Alert Logic agent-based scanning provides the most effective and efficient vulnerability scan with minimal impact on a host; it requires no credentials management and offers low resource consumption. 

Network scanning – which includes authenticated and unauthenticated scanning – initiates from an appliance and goes through the network to a target host.  

• Unauthenticated network scanning assesses exposed ports, protocols, and services on the target host to identify vulnerabilities from the point of view of an outside attacker. Networks or hosts can be adversely impacted and the lack of visibility can lead to inaccurate results and missed patch details. 
• Authenticated network scanning utilizes credentials to log into the host to identify vulnerabilities, misconfigurations, and missing patches. There is less impact and network disruption than with unauthenticated networks scans.   

Best practice for full scan visibility includes pairing an unauthenticated network scan with the agent-based scan - which does not require special credentials to get a complete vulnerability picture - or using authenticated network scans.