Column-Level Insider Threat Detection for Sensitive Data

The breach started with a single query. One line of SQL exposed sensitive columns no one thought could leak.

Insider threat detection is not just about watching who logs in. It is about knowing exactly which data they touch, when they touch it, and why. Sensitive columns—fields holding personal identifiers, financial numbers, health records—are the crown jewels of any database. Protecting them means tracking every access, every change, every export.

Most monitoring tools fail at column-level visibility. They see tables, not the specific fields inside them. That blind spot lets rogue queries slip past detection. To close it, you need real-time analysis at the column level. Every select, update, or delete on sensitive columns should trigger logging, context capture, and anomaly scoring.

Detection rules should start with classification. First, catalog sensitive columns across all schemas. Next, identify normal patterns: who usually reads them, from which systems, and at what times. Then, watch for deviations—a developer pulling full client SSNs at midnight, or a service querying health records it never needed before. These patterns form the baseline for insider threat alerts.

The key is precision. Too many alerts and the system becomes noise. Too few and threats slip through. Machine learning can help find patterns, but deterministic rules still matter. For example:

• Flag queries returning more than a threshold number of sensitive rows.
• Block ad-hoc access from non-approved accounts.
• Alert when joins combine sensitive columns with external datasets.

Log retention is critical. Keep historical access logs long enough to trace incidents after discovery. This creates a forensic trail that stands in both technical and legal reviews. Encryption at rest and masking in transit add further layers, but they do not replace detection.

The cost of ignoring column-level monitoring is simple: you will only know about the breach when the data surfaces elsewhere. By then, the damage is done.

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