Answer Description

A virus is a type of malware that infects another program (typically an exe/executable) and has the ability to spread itself to other systems. Both viruses and worms may have the ability to replicate themselves with or without user intervention. They key difference is that a worm is a standalone program while a virus infects an existing program, for example a critical Windows executable.

Wikipedia

A computer virus is a type of computer program that, when executed, replicates itself by modifying other computer programs and inserting its own code into those programs. If this replication succeeds, the affected areas are then said to be "infected" with a computer virus, a metaphor derived from biological viruses.Computer viruses generally require a host program. The virus writes its own code into the host program. When the program runs, the written virus program is executed first, causing infection and damage. By contrast, a computer worm does not need a host program, as it is an independent program or code chunk. Therefore, it is not restricted by the host program, but can run independently and actively carry out attacks.Virus writers use social engineering deceptions and exploit detailed knowledge of security vulnerabilities to initially infect systems and to spread the virus. Viruses use complex anti-detection/stealth strategies to evade antivirus software. Motives for creating viruses can include seeking profit (e.g., with ransomware), desire to send a political message, personal amusement, to demonstrate that a vulnerability exists in software, for sabotage and denial of service, or simply because they wish to explore cybersecurity issues, artificial life and evolutionary algorithms.Computer viruses cause billions of dollars' worth of economic damage each year. In response, an industry of antivirus software has cropped up, selling or freely distributing virus protection to users of various operating systems.