AT-3(4): Suspicious Communications and Anomalous System Behavior

AT-3(4): suspicious communications and anomalous system behavior requirement means you must train your workforce to recognize, avoid, and promptly report suspicious communications (for example, phishing or social engineering) and unusual system behavior (for example, unexpected prompts, unknown processes, or abnormal network activity), and you must be able to prove that training is role-appropriate and recurring. Treat it as an operational control owned jointly by Security Awareness and Incident Response, with measurable completion and reporting evidence. ¹

Key takeaways:

• Define exactly what “suspicious communications” and “anomalous behavior” mean in your environment, then train to those definitions.
• Operationalize reporting: simple intake routes, triage criteria, and escalation paths that align with your incident handling process.
• Keep evidence that stands up in an assessment: training content, targeted assignments, completions, and reporting/triage records. ²

AT-3(4) is an enhancement to security awareness training that focuses on two failure points that drive real incidents: humans receiving malicious messages and humans observing “weird” behavior on endpoints, servers, or applications and not reporting it. The control is not satisfied by a generic annual security training slide deck. Assessors typically expect you to translate this requirement into concrete, environment-specific examples, then show that personnel were trained, that training repeats, and that reporting routes work in practice.

For a Compliance Officer, CCO, or GRC lead, the fastest path is to treat AT-3(4) as a small, testable program: (1) define reportable signals, (2) publish a reporting mechanism that is easy to use, (3) deliver targeted training mapped to those signals, and (4) retain artifacts showing completion and reporting outcomes. Your goal is to reduce time-to-report for suspicious messages and anomalies, and to show control operation through objective evidence, not narrative.

This page gives requirement-level implementation guidance you can hand to a control owner and assess quickly during readiness, internal audit, or a customer assessment against NIST SP 800-53 Rev. 5. ²

Regulatory text

Control reference: AT-3(4): Suspicious Communications and Anomalous System Behavior. ¹

Provided excerpt: “NIST SP 800-53 control AT-3.4.” ¹

Operator interpretation of what you must do: implement security awareness training content that explicitly covers (a) how to identify and handle suspicious communications and (b) how to identify and report anomalous system behavior, then demonstrate that the training is delivered to applicable personnel and is repeatable as part of your training program. The evidence burden is on you: an assessor will ask for training materials and completion records tied to the population in scope. ²

Plain-English interpretation (what AT-3(4) is really asking for)

AT-3(4) expects you to teach people two practical skills:

1. Message hygiene: recognize suspicious inbound/outbound communications and take safe actions (do not click, do not forward externally, report via the right channel, preserve evidence).

2. “Something is off” detection: recognize system behavior that deviates from normal and report it quickly (unexpected MFA prompts, unusual crashes, unknown tools appearing, sudden performance spikes, data access anomalies, etc.).

In practice, you pass AT-3(4) when a random user can explain what to do with a suspected phishing email, and an engineer can explain how to report a production anomaly without opening a ticket that languishes for days.

Who it applies to

Entity context

• Federal information systems implementing NIST SP 800-53 controls. ²
• Contractor systems handling federal data where NIST SP 800-53 is flowed down contractually or used to meet program requirements. ¹

Operational context (who needs the training)

• All workforce members with email/chat access or access to information systems where anomalous behavior could be observed.
• Privileged users and IT/SecOps require deeper “anomalous behavior” scenarios (admin consoles, CI/CD, cloud control planes, EDR alerts).
• High-risk business roles (finance, procurement, executives, customer support) should get role-specific suspicious communication scenarios because they are frequent targets.

What you actually need to do (step-by-step)

Use this as a build checklist you can assign to a control owner.

Step 1: Define “reportable” events for your environment

Create a one-page Reportable Suspicious Communications & Anomalies Standard. Include:

• Suspicious communications examples: phishing, spoofed domains, QR-code lures, invoice fraud, credential harvesting, unexpected attachment types, urgent payment requests, “password expired” prompts.
• Anomalous behavior examples: repeated MFA prompts, new browser extensions, unknown processes, endpoint encryption warnings, abnormal outbound traffic, impossible travel alerts, unexpected admin role grants, unusual data exports.

Make the definitions concrete: “If you see X, do Y within Z channel.” (Avoid hard time SLAs unless your program can meet them consistently.)

Step 2: Map reporting routes to your incident handling intake

Decide how personnel report:

• “Report Phish” button (email client add-in) and/or forwarding to a monitored mailbox.
• Chat-based reporting (security channel) with a required template.
• Hotline/ticket form for non-email anomalies.

Then write triage rules:

• What constitutes “suspicious comms” vs “system anomaly” vs “benign”?
• Who triages (SOC, IT, Security Operations)?
• When to escalate into incident handling.

Align terminology and handoffs to your incident response process so reports do not die in a queue.

Step 3: Build training content that matches your definitions and tools

Your training must reflect the systems your workforce uses. Minimum content set:

• How to spot common lures (sender mismatch, link previews, attachment risk).
• Safe handling steps (do not interact, capture headers/screenshot if needed, report via approved method).
• How to report anomalous behavior with enough context (device, time, what changed, screenshots, error messages).
• What happens after a report (triage, follow-up, no-blame reporting culture).

Role-based modules:

• General workforce: suspicious email, collaboration tools, basic anomaly recognition.
• Technical staff: endpoint and cloud anomalies, access anomalies, how to preserve logs.

Step 4: Assign training to the right populations and make it recurring

Operationalize AT-3(4) inside your security awareness program:

• Assign modules by role group in your LMS.
• Include training in onboarding for new hires/contractors before access to key systems.
• Reassign training on a recurring basis per your training standard.

If you cannot enforce recurrence yet, document your current cadence and the plan to mature it, but expect an assessor to treat missing recurrence as a gap.

Step 5: Test that reporting works (tabletop + live simulations)

Run controlled tests:

• Phishing simulations routed through the exact reporting mechanism you expect people to use.
• “Anomalous behavior” tabletop: a user reports repeated MFA prompts; validate the path from intake to triage to action.

Keep results focused on control operation: did reports arrive, were they triaged, did responders capture evidence, and did you close the loop with the reporter?

Step 6: Document ownership and evidence production

Assign:

• Control owner: Security Awareness lead (primary), with SOC/IR lead as accountable for triage integration.
• Evidence owner: GRC or compliance operations to collect recurring artifacts.

Daydream can reduce friction here by mapping AT-3(4) to a named control owner, a written implementation procedure, and a recurring evidence list that your teams can satisfy on schedule without re-litigating scope every audit cycle. ¹

Required evidence and artifacts to retain

Keep artifacts that show both design and operation:

Training design artifacts

• Training policy/standard showing security awareness includes suspicious communications and anomalous behavior topics.
• Training modules (slides, videos, scripts) with date/version.
• Role-based training matrix (roles → required modules).
• Reporting job aids (one-pager, intranet page, email banner guidance).

Training operation artifacts

• LMS completion reports (by role group; include exceptions and remediation).
• New hire onboarding training assignments and completion.
• Records of periodic re-training assignments.

Reporting and triage operation artifacts

• Samples of reported suspicious messages (sanitized) with timestamps.
• SOC/ITSM tickets created from reports and their dispositions.
• Evidence that reporters received guidance (closure notes, user communications).
• Simulation/tabletop records: scenario, participants, outcomes, corrective actions.

Common exam/audit questions and hangups

Assessors and auditors tend to focus on these points:

1. “Show me the content.” They want to see training materials that explicitly address suspicious communications and anomalous behavior, not general security principles. ²

2. “Who took it?” Expect sampling by role, including contractors and privileged users.

3. “How do people report?” Auditors will ask for the reporting mechanism and evidence that it is monitored.

4. “Does it work?” They may request examples of actual reports, triage outcomes, and evidence preservation.

5. “How do you handle anomalies outside email?” Many programs over-index on phishing and ignore system behavior reporting.

Frequent implementation mistakes (and how to avoid them)

Mistake	Why it fails	Fix
Training is generic (“be careful with email”)	Doesn’t teach actionable detection/reporting behaviors	Train to your actual tools, include screenshots, and publish a reporting SOP
No defined “anomalous behavior” examples	Users don’t know what to report	Publish a short list of reportable anomalies tailored to endpoints, cloud, apps
Reporting route is unclear or unmonitored	Reports never become incidents	Set one primary intake path and confirm monitoring with on-call coverage
Evidence is scattered	You cannot prove operation	Centralize evidence collection (LMS exports, ticket samples, simulation logs)
Technical teams excluded	Admins often see anomalies first	Assign role-based anomaly training to engineering/IT/SecOps

Enforcement context and risk implications

No public enforcement cases were provided in the source catalog for this requirement, so this page does not cite enforcement outcomes.

Risk-wise, under-training on suspicious communications increases likelihood of credential compromise and business email compromise. Under-training on anomalous behavior increases dwell time because early signals go unreported. Your practical exposure is also assessment failure: AT-3(4) is commonly tested through artifact review and interviews, and “we do training” without evidence or role mapping rarely passes.

Practical 30/60/90-day execution plan

Use this plan as an execution checklist. Adjust sequencing to your org’s change management.

First 30 days (establish minimum viable compliance)

• Name a control owner and backups; document RACI.
• Draft the “reportable events” one-pager (suspicious comms + anomalies).
• Decide and publish the reporting channel(s) and triage owner.
• Inventory existing training content; identify gaps for anomalous behavior content.
• Define evidence retention: where LMS exports live, where ticket samples are stored, and who collects them.

Days 31–60 (deliver training + connect to operations)

• Publish updated training modules and job aids.
• Assign role-based training in the LMS, including privileged users and contractors in scope.
• Implement or validate “Report Phish” mechanics and mailbox monitoring.
• Write triage procedures and escalation criteria aligned to incident handling.
• Run one phishing simulation and one anomaly tabletop; log outcomes and fixes.

Days 61–90 (harden and make assessable)

• Close training completion gaps; document exceptions and remediation.
• Tune triage: reduce misroutes, standardize required fields, improve reporter feedback.
• Produce an “AT-3(4) evidence packet” for assessments: content, assignments, completions, reporting samples, simulation results.
• Configure Daydream (or your GRC system) so AT-3(4) has a stable control narrative, mapped owners, and recurring evidence tasks that repeat on a predictable schedule. ²

Frequently Asked Questions

Does AT-3(4) require phishing simulations?

The control text provided here does not mandate simulations, but simulations are a practical way to prove the reporting path works and generate operational evidence. If you do not run simulations, retain other proof that personnel can report and that triage occurs. ²

What counts as “anomalous system behavior” for non-technical staff?

Focus on observable end-user signals: repeated MFA prompts, antivirus/EDR pop-ups, sudden slowdowns paired with fan spikes, unknown extensions, or unexpected login alerts. Pair each example with a simple “report it this way” instruction.

Can we satisfy AT-3(4) with an annual security awareness course only?

You can, if the course explicitly covers suspicious communications and anomalous behavior and you can show completion for the in-scope population. Many annual courses miss the “anomalous behavior” piece or lack proof of role targeting. ¹

How do we scope contractors and third parties?

Include contractors who access your systems or handle federal data in your training population and completion reporting. For external third parties without system access, document why they are out of scope and how you address their risk contractually.

What evidence is strongest for auditors?

A clean chain: training content version, LMS assignment by role, completion exports, and a sample of real or simulated reports that were triaged and closed. Keep artifacts consistent and time-bounded so sampling is easy.

We have multiple reporting channels (email, ticketing, chat). Is that a problem?

Multiple channels are workable if you document the primary path, monitor all channels, and normalize them into one triage workflow. Audits fail when channels exist but nobody owns them.

Footnotes

1. NIST SP 800-53 Rev. 5 OSCAL JSON

2. NIST SP 800-53 Rev. 5