Manual Scan is an on-demand scan.
Manual Scan on Security Agents eliminates threats from files and eradicates old infections, if any, to minimize reinfection.
Manual Scan on Messaging Security Agents (Advanced only) scans all the files in the Information Store of your Microsoft Exchange server.
The time taken for the scan depends on the client’s hardware resources and the number of files to be scanned. A Manual Scan in progress can be stopped by the Security Server administrator if the scan was run remotely from the web console, or by the user if the scan was run directly on the client.
Trend Micro recommends running Manual Scans after a threat outbreak.