The methodology you choose changes what the test actually simulates, how long it takes, and how much ground it can cover — it's not just a stylistic preference.
Testers start with no internal knowledge, simulating an outside attacker with no inside information about your systems, architecture, or credentials. This is the most realistic simulation of an external threat, closely mirroring what an opportunistic attacker scanning the internet would actually experience.
The tradeoff is time: without any starting information, testers have to do their own reconnaissance and mapping before they can even begin looking for exploitable weaknesses, which can mean less depth per hour of testing compared to other methodologies.
Testers work with partial knowledge, such as a standard user credential or limited network access. This simulates what a compromised low-level account, or a malicious insider without elevated access, could actually do once inside your perimeter.
Grey box testing tends to be a practical middle ground for businesses that want realistic results without paying for the full reconnaissance time that pure black box testing requires.
Testers get full access and documentation up front — source code, architecture diagrams, admin credentials, whatever's relevant to the scope. This is the fastest way to get deep coverage, since time isn't spent on reconnaissance and testers can go straight to identifying and exploiting weaknesses.
It simulates a fully informed insider, or an attacker who's already gained deep access through some other means, and tends to surface more findings per hour of testing than black box does.
If you want to know specifically what an outsider could do with zero information, black box is the right simulation. If you want maximum coverage and the most findings in a limited timeframe or budget, white box gets you there faster.
Many businesses run a mix over time — black box periodically to validate the realistic external threat picture, white box more frequently for deep, efficient coverage of specific systems.
If you want to know what an outsider could do with zero information, choose black box. If you want maximum coverage in a limited timeframe, white box finds more in less time. Grey box is a reasonable middle ground for most first-time engagements.
The report format stays consistent, but the findings themselves reflect what each methodology was able to uncover — white box reports tend to be more comprehensive per hour spent, while black box reports more accurately reflect real-world outsider risk.