Purple Team: When It Beats a Red Team

A red team is adversarial and quiet. A purple team is collaborative and loud. The techniques overlap almost entirely; the posture is opposite.

In a purple team exercise the attackers and defenders work in the same room, or the same call. The attacker runs a technique and says so. The defenders look for it. If they cannot see it, everyone stops, works out why, fixes the gap, and runs it again.

The output is a list of techniques you can now detect and could not that morning.

Why it is usually the better first purchase

A red team answers one question: would we notice this? It answers it with one attempt at one route. If the answer is no, you learn that one thing, expensively.

A purple team answers it across dozens of techniques in the same time, and fixes each gap as it appears. When detection coverage is genuinely unknown, which it is for most organisations, that is a far better trade.

The sequence that usually makes sense:

1. Penetration testing, until hygiene findings stop dominating.
2. Purple teaming, to build and verify detection coverage.
3. Red teaming, to test whether that coverage holds against someone patient who is not announcing themselves.

Buying the third before the second usually produces an expensive demonstration of something a cheaper exercise would have shown.

The one prerequisite

A purple team exercise tunes a detection capability. If there is nothing to tune, there is nothing to do.

Concretely, you need somewhere the telemetry lands and somebody who can change a rule. An organisation with endpoint and network logging, a place those logs are searched, and an engineer empowered to write or amend a detection during the week will get everything out of the exercise. An organisation whose logs sit on the hosts that generated them will spend the week discovering that, which is a finding available far more cheaply.

If that describes you, the useful purchase is the logging work first. It is not a failure to be told so.

What an exercise looks like

Techniques are usually selected against a public framework, commonly MITRE ATT&CK, which catalogues adversary behaviour by tactic. That makes coverage measurable.

Selection should follow your threat model and your estate, not the framework's table of contents. A retailer with no Linux servers gains nothing from Linux persistence techniques, and a bank that has never seen a macOS endpoint should not spend a morning on one. The right list is short, relevant, and weighted towards the tactics that appear early in a real intrusion, because those are the ones where detection still buys you time.

For each technique: the attacker runs it, the defenders check their tooling, and the result is recorded in one of three states.

• Detected. Something alerted, and a human would have seen it.
• Logged but not alerted. The data was there and nothing drew attention to it. This is the interesting category and usually the largest. It is a tuning problem instead of a coverage problem, and it is frequently fixable the same day.
• Invisible. No record at all. That is a logging gap, and fixing it is engineering work that will outlast the exercise.

Where a gap is found, it is fixed and the technique re-run. That loop is the whole point, and an exercise that records outcomes without re-running is an audit wearing the name.

What you get

A coverage matrix: techniques down one axis, your detection outcome across the other. Run it again in six months and the difference is the measurement.

Two things make that matrix keep its value. The detections written during the week belong in version control with everything else, because an undocumented rule that somebody tuned on a Thursday is the first thing lost in a platform migration. And the invisible column is a backlog, not a verdict: it is the list that justifies the next piece of logging work to whoever signs for it.

A security team gets considerably more out of this than out of a narrative about one successful intrusion. A board gets considerably less. Decide who the report is for before you commission either.

Where it goes wrong

• Nobody in the room can change anything. If the detection engineer is a ticket away, the loop breaks and the exercise degrades into a list of gaps somebody will look at next quarter.
• It is run as a demonstration. A vendor executing techniques while your team watches is a product demonstration. The defenders have to be the ones hunting, and being unable to find something is the expected outcome for part of the week.
• The technique list came from the framework. Coverage of things that will never happen to you measures nothing.
• The result is filed. The matrix is an input to the next quarter's engineering plan. Filed, it is a document about a week in March.

Tooling that automates the attacker half

Breach and attack simulation platforms run catalogued techniques on a schedule, and they cover the repeatable part of this work well. What they do not do is the conversation: the part where an engineer works out why the telemetry was there and the alert was not, and changes something. Treat the tooling as a way to keep a coverage matrix current between exercises instead of as a replacement for one. The comparison is in adversary simulation and breach-and-attack simulation.

For SEBI-regulated entities there is a specific point to know here. The technical clarifications of 28 August 2025 restated the relevant CSCRF provision so that a range of solutions including threat simulation is recommended in consultation with the IT Committee, and the acronyms BAS and CART no longer appear in the text. A buyer should know they are choosing these capabilities on their merits. The detail is in red teaming and SEBI CSCRF.

When a red team is genuinely the right answer

• Detection coverage is already measured and believed to be good, and the question is whether it survives someone patient.
• Response is being tested instead of detection: whether alerts get acted on at two in the morning.
• Something outside technical controls is in question: people, premises, suppliers.
• An external requirement names an adversarial exercise specifically.

The full comparison with penetration testing is in red team versus penetration testing, and what an adversarial exercise reports back about your defenders is in what the exercise tells you about detection.