Aptly named
Well, I'm sick. So what you ask? I'm not really digging for sympathy, and (as the people who try to help me find out) really just prefer to be left alone to let my body fight it. However, something just made me think that calling a computer virus a virus is very, very good naming. A biological virus that makes you sick, and a computer virus have much of the same characteristics.
First off, I'm slow. Ever since yesterday I haven't wanted to do anything. Even on a computer, I have no drive to program and that's minimal (physical) effort. my brain just wants to do nothing. For a computer, the virus ties up your CPUs time (depending on the type) and slows things down. Get more than one in there, and you now have a brick of a machine.
I'm also (if my diagnosis is correct) probably contagious. I can spread my disease to other humans of roughly the same type within a certain radius and by certain vectors. This is exactly the same as computer virii. They spread via some vector (email, ip scanning, whatever) to other computers of roughly the same type. Just as some people from foreign countries have immunities to certain attacks, so too does certain operating systems. A worm bred for Windows won't infect my Linux machine, in the same way that a virus attacking a machine with Apache's server installed won't affect IIS.
Then, each disease has different symptoms. Mine include being sore and having a headache. Computer virii have different symptoms as well which are side effects of whatever the virus is doing. Some may simply slow the computer down. Others will delete files, or lock certain menus.If I know a certain virus well, and see a computer displays its symptoms I can guess its my old friend MyDoom.
Virii are killed through certain medications. In humans, that's obvious, in computers those medications take the form of anti-virus softwware. It knows what files to delete to kill a virus, or what process must be taken to clean the system. Computers can also be immunized like humans by locking certain files that can expect infection by certain virii. This paragraph sucks because I'm about out of steam and already finished the post.
Finally, every virus behaves differently. Rather: It is not guarenteed that every virus will be the same. Each human disease does soemthing different. Some feed off brain tissue, others just live on your skin. In the same way, each computer virus does something different. Some delete files at random on certain days. Some watch what keys you type. Others are just broken and do nothing. The motivation of the virus is what determines its behavior.
To give an example of how varied computer virii are, here's a link to a nice list of many different types.
