How long do viruses take to reproduce themselves?
It depends only on the virus itself. In general, they try to infect as fast as possible, although in many cases they can only infect under certain circumstances such as specific dates or specific files. They also try to avoid infecting the same file more than once. The speed of infection also depends in part on the type of virus in question. In particular, it depends very much on whether the virus is memory-resident or not.
