What a virus cannot do on its own in computers?

Like a real world virus, Computer Viruses heavily rely on a "host" file in order to propagate. In the wild, if a computer virus cannot attach and inject itself into a host file, it will just roam around and eventually get destroyed by an antivirus program. Computer viruses cannot replicate without a host. Worms on the other hand are independent programs that can replicate freely without the need of a host like a virus. When it comes to lethality though, a virus is more destructive than a worm.