What is a security assessment?
A security assessment builds upon a vulnerability assessment by adding manual verification of the results to confirm the level of exposure. It does not though include the use of exploitation code to gain further access to systems.
What do you get?
A security assessment is looking to gain a broad coverage of the systems under test but does not consider the depth of exposure to which a specific vulnerability could lead. False positives should be excluded through the analysis of the results. Security assessments are great for exposing business logic flaws and identifying security vulnerabilities that automated tools are unable to identify. This leads to a higher level of assurance. However, the time and effort required to complete a security assessment are higher than vulnerability scanning and assessments and require a higher level of technical skill to deliver.