When we talk about what is the main difference between a virus and a Trojan, traditionally a virus is malware that uses the infected host to replicate itself to other systems, i.e. by infecting files that might get shared, copying itself to network drives or USB sticks. It gets usually is not knowingly executed by the user but gets executed when the user opens an infected file, runs an infected program, etc.
What is the main difference between a virus and a trojan?
A computer virus attaches itself to a program or file so it can spread from one computer to another, leaving infections as it travels. Much like human viruses, computer viruses can range in severity: Some viruses cause only mildly annoying effects while others can damage your hardware, software, or files. Almost all viruses are attached to an executable file, which means the virus may exist on your computer but it cannot infect your computer unless you run or open the malicious program. A Trojan horse is not a virus. It is a destructive program that looks like a genuine application. Unlike viruses, Trojan horses do not replicate themselves but they can be just as destructive. Trojans also open a backdoor entry to your computer which gives malicious users/programs access to your system, allowing confidential and personal information to be theft. A trojan on the other hand is malware that claims to be something different, like some malware claiming to be a virus scanner. It counts on the user to execute it knowingly by believing what the software claims to be.In common language often any kind of malware is simply called a virus, i.e. real viruses, trojans, ransomware, etc. For example, a virus scanner also cares about all types of malware, not only viruses.
