By design, the manual scan will include Windows system files (including hidden protected system files) when scanning a single file or folder to ensure system security.

To improve scan performance, the scan engine uses a cache mechanism, which allows it to remember the state of the files that have been scanned. If a threat-free file has been scanned and has not been modified for a period of time, it will be skipped on the next scan. However, the file will be scanned again if it was recently modified.