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Do not reset or download a project simply to make a mismatch disappear. A download or memory-clearing recovery can disrupt the process and erase data or configuration. Rockwell Automation’s SD1790 security advisory, revision 5.0, updated September 18, 2026, describes threat activity targeting internet-exposed MicroLogix 1100 and 1400 controllers, including configuration tampering and passwords set without the owner’s knowledge.
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What counts as a suspicious change?
A difference between the running controller and an approved offline project warrants investigation, but it does not establish who made the change or why. Legitimate maintenance, a project revision, or changes in live data can explain some differences. Investigate the context before deciding that a discrepancy is unauthorized.
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Do not assume every MicroLogix provides a complete audit trail, a tamper alarm, or one universal automatic compare command. Rockwell’s advisory recommends monitoring for unexpected connection attempts, mode changes, and downloads, but the reviewed documentation does not establish complete, tamper-evident history on every model and software revision.
How to investigate safely
1. Coordinate with operations and preserve the current state
Before connecting to the controller or changing its mode or program state, notify the process owner and follow site safety, incident-response, and change-control procedures. Even an online program edit can have unexpected effects on controlled equipment; the MicroLogix 1100 User Manual (1763-UM001G, May 2024) cautions users about this risk.
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Record the exact catalog number and series, firmware, operating mode, IP and network configuration, alarms, time, and relevant maintenance or authorization context. Preserve available project files, configuration, records, and screenshots as separate, timestamped evidence copies. Do not reset the controller, download a project, or accept an overwrite prompt before an approved recovery plan is in place.
2. Establish the right approved baseline
Find the approved offline project for the specific machine and controller—not merely a project for a similar MicroLogix. Record its revision, date, owner, and how its approval and integrity were established. Preserve the original file unchanged; use a separate evidence copy for comparison.
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Use a programming environment compatible with the controller and its documentation. Rockwell identifies RSLogix 500 as programming software for MicroLogix 1400. Before any authorized read or upload, verify the connection identity so you do not collect from or program the wrong controller. Follow the site’s approved procedure: even a read operation should be planned so it does not accidentally alter controller state.
3. Compare and investigate differences
Where authorized and safe, read the controller’s current image into a new evidence copy. Compare that copy with the approved baseline using the supported features of the installed software version. Do not overwrite either file while investigating.
Review logic and relevant configuration separately. Examine data, forces, mode, and network settings as distinct evidence; live values can change during normal operation. Check maintenance and change-control records, along with available network or controller records, for context such as unexplained connections, mode changes, or downloads. Record what differs, when it was observed, and which evidence supports or contradicts an unauthorized-change hypothesis.
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4. Contain and restore only with an approved plan
Coordinate any isolation or transition to Program mode with operations; changing connectivity or mode can affect the process. If unauthorized changes are confirmed, retain the suspected controller image and investigation notes. Restore only from a verified project matched to the controller hardware, series, and application, and plan how to re-establish required configuration and validate process behavior.
Do not use a factory reset or memory-clearing procedure as routine logic cleanup. Unknown-password recovery is a separate, destructive situation and must follow the current Rockwell procedure for the exact model and series. SD1790 warns that the MicroLogix 1400 recovery clears the application program, data, and network/IP configuration; the MicroLogix 1100 procedure clears the program and password.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why the recovery procedure depends on the model
Rockwell’s SD1790 describes different unknown-password recovery paths for the covered MicroLogix 1400 and 1100 series. These are not ordinary methods for removing a suspected logic change: both involve clearing program memory and require a known project and a planned restoration.
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| Controller | SD1790 recovery path for an unknown password | Stated impact and follow-up |
|---|---|---|
| MicroLogix 1400, Series A, B, or C | Clear application memory through the battery-removal procedure specified by Rockwell. | Erases the application program, data, and network/IP configuration. Restore IP configuration and download a known project. |
| MicroLogix 1100, Series A, B, or C | Use Program mode and a ControlFLASH firmware update over DF1 serial, following Rockwell’s specified procedure. | Clears the program and password; redownload a known project. |
These summaries do not replace the exact procedure in the current advisory. Confirm the controller’s catalog number and series, the applicable firmware and connection requirements, and the availability of a verified project before recovery. For the 1400 procedure in particular, plan for the stated loss of IP configuration as well as program and data. Do not remove a battery, change mode, or run a firmware update without site authorization and the applicable Rockwell instructions.
How to reduce the chance of recurrence
- Remove direct internet exposure to control devices. Place them behind firewalls and restrict communications to trusted engineering workstations and known IP addresses.
- Keep offline backups of approved projects and relevant configuration, with clear revision, ownership, and change-approval records.
- Monitor available records for unexpected connection attempts, mode changes, and downloads; retain those records according to site policy.
- Use passwords as one layer, not as the sole security control. Rockwell’s SD1790 states: “Setting a password alone is not sufficient mitigation and should be combined with additional hardening steps referenced in this document and otherwise as appropriate to the risk of the deployment.”
- Check applicability before using firmware- or series-specific security features. SD1790 names Enhanced Password Security for MicroLogix 1400 Series B with FRN 21.002 or later; verify the exact model, firmware, and current advisory before applying it.
Rockwell’s MicroLogix 1400 Reference Manual (1766-RM001J, June 2023) also warns against relying on password protection alone. A data-file download-protection feature described in the MicroLogix 1100 Reference Manual (1763-RM001D, September 2011) concerns data retention and file limitations; it should not be treated as a logic-change detector.
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