A virus requires a legitimate program or file to attach to, much like a medical virus requires cells to host it.
Typically, a virus will remain inactive, attached to the host program or file, until something causes the virus to become active, which might be the program being run or the file being access or opened.
How does a computer virus work?
A virus needs a host program or file in order to run (or 'execute').
When the program or file is accessed, the computer is instructed to execute certain operations to fulfil the instruction, and in turn the virus can also execute.
How does a Virus Spread?
Viruses can be spread through email attachments, visits to websites, downloaded files and links in emails or other messages.
When a virus executes on a computer, it will perform malicious tasks on that computer (called 'releasing the payload'), but will also seek a means of spreading or propagating to other parts of the infected computer, and to other computers.
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