A server has been infected by a certain type of Trojan. The hacker intended to utilize it to send and host junk mails. What type of Trojan did the hacker use?

Turtle Trojans is not a recognized or standard Trojan classification in cybersecurity taxonomy.

Ransomware Trojans encrypt victim data and demand payment for decryption keys - they are not used for spam distribution or mail hosting.

A Botnet Trojan infects a system and connects it to a command-and-control (C2) network, making the host a 'bot' in a larger botnet. Botnets are commonly weaponized for spam campaigns, hosting phishing pages, and distributing malware at scale. The scenario of sending and hosting junk mail is a textbook use case for botnet infrastructure.

Banking Trojans are designed to steal financial credentials and intercept banking sessions, not to send or host junk mail.