Final answer:
A trojan is a type of malware that users are typically tricked into installing, thinking it is legitimate software. Once activated, they can cause harm by allowing cyber-criminals to access the system. The correct statement about trojans is that they are installed by the user.
Step-by-step explanation:
A trojan is a type of malicious software or malware that is often disguised as legitimate software. Trojans can be used by cyber-thieves and hackers to gain access to users' systems. Users are typically tricked by some form of social engineering into loading and executing Trojans on their systems. Once activated, Trojans can enable cyber-criminals to spy on you, steal your sensitive data, and gain backdoor access to your system.
Among the options provided:(b) 'Infects the boot sector' is not typically associated with trojans; this is more characteristic of a boot sector Unlike anti-virus software, trojans do not protect against adware. Adware is a type of software that displays unwanted advertisements on the user's computer. While there are some security software that can help detect and remove trojans, it is important for users to exercise caution and avoid downloading or opening unfamiliar files to prevent infections.