Comprehensive and Detailed in-Depth Explanation:

Understanding the Risk Levels:

Inherent Risk:

Theoriginal riskbefore any controls or mitigation measures are applied.

In this scenario, it represents therisk of automated purchases without CAPTCHA.

Residual Risk:

Theremaining riskaftermitigation strategieshave been applied.

After implementing CAPTCHA, some risk remains asCAPTCHA systems can be bypassedorhuman-operated botsmay still make purchases.

Mitigated Risk:

A risk that has beenreduced or managedeffectively.

While CAPTCHAmitigatesthe issue, it does noteliminateit.

Low Risk:

A risk that is consideredminordue to effective mitigation or low impact.

CAPTCHA reduces risk but does not guarantee it is low.

Transferred Risk:

A risk that has beenshifted to another entity, such asoutsourcing or insurance.

Implementing CAPTCHA does nottransfer riskbut ratherreduces it directly.

Why the Correct Answer is D (Residual):

Implementing CAPTCHAreduces the number of automated purchases, but therisk is not entirely eliminated.

There is always aresidual riskbecause:

Advanced botsmay bypass CAPTCHA systems.

Human-assisted purchasesmight still occur, as attackers might hire people to complete CAPTCHAs.

Therefore, the risk after implementing the CAPTCHA system isresidual, assome potential for automated purchases remains.

Why the Other Options Are Incorrect:

A. Inherent:

Inherent risk existsbeforeany mitigating actions, like CAPTCHA implementation.

Since the CAPTCHA is already suggested, we are addressing theresidual risk.

B. Low:

While CAPTCHA reduces the risk, itdoes not eliminate it completelyor make it negligible.

Attackers can stillbypass CAPTCHAusing more sophisticated methods.

C. Mitigated:

The CAPTCHA reduces risk butdoes not fully mitigate it.

The termmitigatedimplies a more comprehensive reduction than what CAPTCHA alone can provide.

E. Transferred:

There isno transfer of riskto another party or system.

CAPTCHA directlymitigatesrisk rather than shifting responsibility.

Real-World Scenario:

Whenpopular productsare released (like new GPUs), attackers usebotsto make bulk purchases.

Retailers implementCAPTCHA systemsto prevent automated orders.

However,bot developerscontinuously innovate tobypass CAPTCHA, leaving some level ofresidual risk.

Extract from CompTIA SecurityX CAS-005 Study Guide:

TheCompTIA SecurityX CAS-005 Official Study Guidedefinesresidual riskas therisk that remains after controls are implemented. Implementing aCAPTCHAsystem reduces thelikelihoodof automated purchases butdoes not fully eliminate the threat, thus leaving aresidual risk.