CMMC Practice SI.1.213
Perform periodic scans of information systems and real-time scans of files from external sources as files are downloaded, opened, or executed.
Bold Coast Security Guidance
This practice is an extension of SI.1.211, and specifies more configuration requirements, in this case, the need to automatically scan new files and devices automatically, and to schedule regular full scans of the devices at regular intervals, usually daily.
Your policy will note the requirement to automatically scan files and devices, and the interval for your full scans. You should also define who gets alerted in your plan if action is taken to quarantine, clean, or delete an infected file. You will need to check the effectiveness of this control for maturity level four by regularly verifying scans are taking place as expected.
DRAFT NIST SP 800-171 R2
Periodic scans of organizational systems and real-time scans of files from external sources can detect malicious code. Malicious code can be encoded in various formats (e.g., UUENCODE, Unicode), contained within compressed or hidden files, or hidden in files using techniques such as steganography. Malicious code can be inserted into systems in a variety of ways including web accesses, electronic mail, electronic mail attachments, and portable storage devices. Malicious code insertions occur through the exploitation of system vulnerabilities.
Malicious code protection mechanisms include anti-virus signature definitions and reputation-based technologies. Many technologies and methods exist to limit or eliminate the effects of malicious code. Pervasive configuration management and comprehensive software integrity controls may be effective in preventing execution of unauthorized code. In addition to commercial off-the-shelf software, malicious code may also be present in custom-built software. This could include logic bombs, back doors, and other types of cyber attacks that could affect organizational missions/business functions . Traditional malicious code protection mechanisms cannot always detect such code. In these situations, organizations rely instead on other safeguards including secure coding practices, configuration management and control, trusted procurement processes, and monitoring practices to help ensure that software does not perform functions other than the functions intended.