A Trojan is malicious software that disguises itself as a harmless application in order to gain access to computers and carry out harmful activities there.
Unlike viruses, Trojans do not multiply on their own, but hide in supposedly useful applications. They often enter computers via fraudulent emails, fake antivirus programs or unsafe downloads. There are different types of Trojans, including backdoor, banking, DDoS and blackmail Trojans.
To protect themselves, users should update their software regularly, avoid suspicious links and attachments, use complex passwords, enable two-factor authentication and use security software. Regular backups and only downloading software from trustworthy sources are also recommended.