Final answer:
In vulnerability scanning, a proxy is used to keep the scan hidden from network defenses by obfuscating the scanning source, which allows for more thorough vulnerability assessments.
Step-by-step explanation:
When conducting vulnerability scanning, the purpose of using a proxy is primarily to keep a scan hidden. By routing the scanning traffic through a proxy server, the actual source of the scan is obfuscated, which can be useful for security professionals who need to simulate an attack without being detected by network defenses or alerting the target. Using a proxy can also assist researchers in bypassing IP-based access and rate controls, allowing for more thorough testing of the target system's vulnerabilities.