How Does the Virus Know When to Attack and What Happens When it Does?
Anything can trigger the virus to attack. It is programed to attack after a certain task has been completed. Most viruses are programmed to attack after a certain time is reached, or a specific date is reached, or even when the virus replicates it self a specified number of times.
Once the virus does attack the effects can be anywhere from a message being displayed on the screen, or hard drive corruption to the point of not being able to access it.