A rootkit (Option A) is a type of malware designed to gain administrative (root) access to a system while hiding its presence. Rootkits can manipulate system processes and files to remain undetected, making them particularly dangerous. * Trojan (Option B) is malware disguised as legitimate software but doesn't necessarily provide administrative access. * Worm (Option C) spreads across networks but doesn't grant administrative access. * Ransomware (Option D) encrypts data and demands a ransom but doesn't typically provide ongoing administrative access. CompTIA A+ Core 2 References: * 2.3 - Explain malware types, including rootkits and their purpose .