A privacy engineer has been asked to review an online account login page.

Option A (Implement a CAPTCHA system): CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) helps to prevent automated bots from attempting unlimited login attempts, reducing the risk of brute force attacks. It effectively adds a layer of security by ensuring that login attempts are made by humans, not automated scripts.

Option B (Server-side input validation checks): While important for overall security, input validation checks do not specifically address the issue of limiting invalid login attempts.

Option C (Enforce strong password and account credentials): Strong passwords and credentials are important but do not directly limit the number of invalid login attempts.

Option D (Implement strong TLS): Transport Layer Security (TLS) ensures encrypted communication but does not limit the number of login attempts.

References:

OWASP (Open Web Application Security Project) guidelines on preventing brute force attacks.

NIST SP 800-63B Digital Identity Guidelines on authentication and brute force protection.

Conclusion: Implementing a CAPTCHA system (Option A) is the best recommendation to minimize the potential privacy risk from unlimited invalid login attempts, as it helps to distinguish between human and automated login attempts, reducing the risk of brute force attacks.