After installing a backdoor on a web server, what action best ensures it remains undetected?

In CEH v13 Maintaining Access, stealth and persistence are key goals after compromise. Placing a backdoor in a file type excluded from resource maps (such as image metadata, configuration files, or uncommon extensions) reduces the likelihood of discovery by automated scanners and integrity checks.

Option D is correct because many security tools focus on executable or commonly accessed web files. Files excluded from resource maps are less likely to be scanned or monitored.

Option A increases detection risk due to frequent changes. Option B increases signature visibility. Option C still exposes the file to access logs and monitoring.

CEH v13 highlights that attackers often hide backdoors in non-obvious locations to avoid detection. Therefore, Option D is correct.