The ApacheErrorDocument directive should be set correctly for HTTP 404 errors.
(1) message/document
(1) Apache configuration file: 'ErrorDocument 404' directive
L1 11. Web Server Software Obfuscation General Directives p17
2.7 Additional Software Information Leakage Protection p50
CIS Apache Benchmark for Unix v1.7 For Apache Versions 1.3 and 2.0
CIS
2007-07-01
Version 1.7
Prose (PDF)
Security Configuration Benchmark For Apache Web Server
CIS
2008-11-01
Version 2.2.0
Prose (PDF)