Any information revealed in an HTML comment might help an adversary learn about the system and form a plan of attack.
HTML comments provide an attacker with an easy source of information about a dynamically generated web page.
Example 1:
<!-- TBD: this needs a security audit -->
<form method="POST" action="recalcOrbit">
...
[1] Standards Mapping - OWASP Top 10 2007 - (OWASP 2007) A6 Information Leakage and Improper Error Handling
[2] Standards Mapping - Security Technical Implementation Guide Version 3 - (STIG 3) APP3620 CAT II
[3] Standards Mapping - Common Weakness Enumeration - (CWE) CWE ID 615
[4] Standards Mapping - Web Application Security Consortium 24 + 2 - (WASC 24 + 2) Information Leakage
[5] Standards Mapping - Payment Card Industry Data Security Standard Version 2.0 - (PCI 2.0) Requirement 6.5.5
[6] Standards Mapping - Payment Card Industry Data Security Standard Version 1.2 - (PCI 1.2) Requirement 6.5.6