Codeman said it well, if I made add some more words...
A brief comparison to human immune system:
1. Barriers
All portals (skin, respiratory, digestive, etc) have barriers in place that limit bacterial growth, impede invader movement, poisons, etc.
2. Inflammation
Body cells being attacked by marauders call for help. The cells know they are being attacked when certain parameters for themselves are not being met. When they call for help, the police show up, which are the next 2 steps.
3. Expert on self
The white blood cells, etc are adapt at recognizing cells that belong in the body. At this stage, they detect counterfeits by being experts in the original. When an invader is detected, it is remembered. The police first check the identification of the offender.
4. Memory of past invaders
When an invader is detected, it is often remembered so it can be detected more quickly in the future. In that case, the invader is compared to a known list of offenders. This can be quicker in some cases than waiting for a detail comparison to known law-abiding cells.
--
The current internet already has many similarities. Firewalls, filters, passwords and security certificates act as first line defense barriers. Computers that have been attacked call for help to central authorities that send out systems that look for known offenders and detect new offenders by contrasting them to a healthy system.
These systems can be improved but they where will always be a balance between invaders and healthy code. In the human body, the immune system has more mass than the brain. The brain also has many defense mechanisms of its own against physical and idea viruses (memes), which incidentally probably have killed more people than physical viruses.
--
The internet is just a communication system. It is more versatile than many other types of communication systems because of its ability to communicate a rich set of tokens, time shift those tokens, lower costs to participate in the conversation, etc.
This communications medium is an expression of the human mind. Just as there are boundaries between our minds, so there are boundaries between the internet and the minds that communicate over it. These boundaries produce an illusion of autonomy. So within this understanding, the internet could be thought of as a body with an immune system protecting its individual cells (the humans and computers connected to it).
Even when the internet becomes more automated, automation is still an expression of the mind. And if my expression effects your expression, then we are in communication. Sometimes people say things without considering all the consequences. Those consequences could range from mild embarrassment to killer robots. Not funny.
Malware is a harmful type of communication. It employs both direct expressions and less direct (more automated) expressions. When a virus attacks your computer, it is basically a human sending a message to a human. Some malware is a message to the good program writers. Other malware is sent directly to the operators (phishing, spam, etc).
It could be said that the first part of the Information Revolution was about increasing communication and the next part is ironically, about decreasing some of that communication. We found out we didn't want to talk to everyone about everything. People don't always say what you want to hear. No, I don't want to hear about your penny stocks…
Since they often require an answer, we have them, "talk to the hand because the ear isn't listening". This is when we have someone else answer their words with words we endorse. These "hired guns" are the defense writers and their automation.
How can mere communication steal from you? The word of one can trap the word of another and they agree to give up the control of resources. This happens at many levels and effects resources like labor, hard disk space, money, knowledge, etc. Botnets (topic?) are a method by how one person's word is trapping many other people's words and leads eventually to the loss of resources.
--
So in a way the internet as a whole acts like a body with the individual computers as cells. This is both a problem and a fact of life. The problem being that is it normal for individual cells to be sacrificed. At any given point, million of cells are being attacked and damaged by invaders while the system as a whole is fairly healthy.
From the sacrificed cell's perspective however, this is not so reasonable. A person could loose 6 months of work on their computer. Not a big loss for the internet as a whole, but a big loss for that person. One method is redundancy- don't just own one cell. Another is to move your cell to safer areas of the system (move further away from the ports, etc) but that has it disadvantages. Another is to try to make your cell act as a complete body, but by doing that, you may loose some adaptability. "No man is an island."
Peter