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 If this replication succeeds, the affected areas are then said to be "infected" with a computer virusComputer 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 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
Computer_virus - Wikipedia, the free encyclopedia