By nDir 
Every scanning programme produces findings that are not true, and how you handle them decides whether the data stays useful. Dismiss too readily and real issues get buried in the same pile. Investigate everything and the team stops looking altogether. NIST’s technical guide to security testing, SP 800-115, treats validation as a distinct phase for this reason: a finding is a hypothesis until somebody checks it.
Why scanners get it wrong
Most false positives come from version-based detection. The scanner reads a package version, compares it against a vulnerability database, and reports a match. On enterprise Linux distributions the security fix is often backported into the same version number, so the software is patched and the version string says otherwise. Web application checks produce their own variety: a firewall returning a uniform error page can make every injection test look successful, and a page that reflects input harmlessly can be flagged as scripting. Neither means the tool is bad. It means the tool cannot see what you can.
Verifying without spending a week
Check one instance properly, then apply the answer to the group. For a backported package, the distribution’s own security tooling will confirm whether the fix is present, and that single check clears every host running the same build. For a web finding, reproduce the request by hand and look at what actually comes back. Keep the evidence with the decision, because the same finding will reappear next month and you do not want to repeat the work or rely on somebody’s memory of a conversation.
“The habit that ruins scan data is bulk marking things as false positives to make a dashboard look better before a board meeting. I have picked up engagements where a genuine critical finding had been suppressed a year earlier as part of a clear-out. Record who decided, when, and on what evidence, or the suppression list becomes a place where risk goes to hide.”
William Fieldhouse, Director, Aardwolf Security Ltd
False positive is not the same as accepted risk
Keep the two decisions apart, because they carry different obligations. A false positive means the finding is wrong and there is nothing to fix. An accepted risk means the finding is real and you have decided not to act, which needs an owner, a reason, an expiry date and sign-off at the right level. Mixing them produces a suppression list that looks like technical noise and actually contains business decisions nobody senior has seen. Auditors ask about the second category, and a tidy record of it turns an awkward conversation into a short one.
Keeping the tooling honest
Track your false positive rate as a quality measure over time. A rate that climbs suggests templates need tuning or credentials have stopped working, since an unauthenticated scan guesses more and guesses wrong more often. Review suppressions quarterly and expire them, so a decision made about a system in 2024 does not silently apply to its replacement. Where a finding is genuinely contested, ask an independent testing provider to attempt exploitation, and use regular vulnerability assessment and scanning to confirm that the resolution holds after the next patch cycle.
Frequently asked questions about false positives
These questions come up when a scanning programme starts producing too much noise.
Should you suppress findings globally or per host?
Per host, or per group where you have verified one member and the build is identical. Global suppression of a check is how a genuine instance on a different platform disappears from view.
Who should approve a false positive?
Someone other than the person who raised it, ideally with the evidence attached. It does not need a committee, and it does need a second pair of eyes to keep the process honest.