A Trojan, short for 'Trojan horse,' is a type of malicious software that pretends to be a legitimate program or file to deceive users into installing it. Once activated, a Trojan can steal personal data, give hackers remote access, or damage the infected device. Unlike viruses or worms, Trojans do not replicate themselves but rely on tricking users to spread. They are often distributed through email attachments, fake software downloads, or compromised websites. Because they appear harmless, Trojans can bypass many basic security measures, making them a significant threat to both individuals and organizations.