>what is the opposite for the virus?
What is a virus? It's basically a program that propagates itself, "infecting" the target computer. The opposite of a virus would be any program that doesn't multiply on its own at all.

You might also define a virus as a self-multiplying program that has a malicious payload[1]. In that case the yang to a virus' yin would be a self-multiplying program that has a beneficial payload. In this case it wouldn't be the defining characteristic of a virus that specifies an opposite, but the intention in which the program is written.

[1] I wouldn't, but you might.

I wouldn't say that malicious payload is a requirement for a virus. So I would just say that the opposite to a virus would be a program that tried to remove all copies of itself

Virus definition:

They replicate quickly
Viruses "phone home"
Viruses use up system resources - making your system slow and causing the user to think they need new hardware
Viruses may trash your hard disk
Viruses can lead to system instability
Often installed without the users permission
Viruses may take your money

Does that make ms windows a virus ?

>>Viruses may trash your hard disk
Oh yes -- what was a feature built into MS-DOS 6.X and Windows 95. I can't count the number of times I had to reformat the hard drive and reinstall everything from scratch.

I have not had that problem since Windows 2000.

my nt4 server system has been running for ~4 years without crash.

NT based is far > DOS based

i want to know whats is the opposite of the virus

Opposite how?

A regular program works as advertised, a virus doesn't.

A regular program is open about it's functionality, a virus isn't.

A regular program doesn't cause damage (usually anyway), a virus usually does. The damage can take many forms, from the machine running a bit slow to complete loss of data, or maybe even data theft.

A regular program is usually installed with full user knowledge, a virus infects automatically or via "social engineering" of the victim (eg, email saying "play this fun game").
Additionally, a virus also has the means to propagate itself.

Clinically speaking, the opposite of a virus is a vaccine. So a vaccine program is one which goes round killing off virus programs.

MS Windows isn't a virus. A virus does something.

i get it the opposite of the virus is a helpfull program like MS windows and microsoft office.