Once the virus is in your computer, you would be surprised how difficult it is to remove it. One of my business associates continues to be plagued with his virus weeks after he found it in his computer. Even the experts are unable to help him get rid of it completely.
Most viruses use email to get from one computer to another.
In most cases the virus is picked up by someone without virus protection on their computer from an infected source. They in turn send an email to a friend, not realizing that the virus has embedded itself into their email program. Now the second party has the virus and is passing it along with every message they send. Your computer will begin crashing or doing any number of weird things. You may even have problems starting up your computer.