What characterizes a Parasitic Virus?

A parasitic virus is characterized primarily by its ability to attach itself to executable files, which allows it to launch together with the application it has infected. This method of infection ensures that when the user runs the infected application, the parasitic virus is also executed. This behavior makes it particularly stealthy because it takes advantage of the legitimate application to proceed with its malicious activities, such as replicating itself or attempting to damage system operations, often without the user's awareness.

The other choices describe different characteristics more associated with other types of malicious software. For instance, the idea of overwriting critical system files is more in line with destructive viruses aiming to cause immediate damage, while mutating to avoid detection refers to polymorphic viruses that change their signatures to evade antivirus software. Creating a copy in memory is a trait that might associate with other forms of malware or specific behaviors rather than characteristic of a parasitic virus itself. Thus, the main identifying feature of a parasitic virus is its integration with legitimate applications during execution.