A penetration tester is tasked with mapping an organization's network while avoiding detection by sophisticated...

CEH v13 highlights the Idle Scan as one of the stealthiest reconnaissance methods available, designed specifically to avoid detection by IDS and security monitoring tools. Idle scanning leverages a “zombie host”—a system with a predictable IPID sequence—to route all probe packets through it. Since no packets ever originate directly from the attacker’s IP, IDS systems are unable to attribute the port scan to the attacker. CEH emphasizes that this technique creates zero direct traffic between the attacker and the target, making it extremely evasive and ideal for highly monitored networks. FIN scans (Option A) are somewhat stealthy but still originate from the attacker and are detectable. TCP Connect scans (Option C) are the most detectable because they complete full connections. ICMP Echo scans (Option D) are easily logged and flagged by IDS. Idle scanning is uniquely suited for bypassing advanced detection systems while still identifying open ports and live hosts.