Is antivirus software necessary

I just install windows XP service pack 3 on my computer and necessary software. But still i didn't install antivirus in my computer i don't think this will create any issue. Is antivirus software necessary ?

Antivirus (or anti-virus) software is used to prevent, detect, and remove malware, including computer viruses, worms, and trojan horses. A computer virus is a program written in order to spread to other computers embedded in legitimate programs called "guests." It may also have the effect, wanted or not, to harm by disrupting more or less seriously harm the functioning of the infected computer. It can spread through any medium of exchange of digital data such as the Internet, as well as diskettes, CDs, USB keys, etc.
Such programs may also prevent and remove adware, spyware, and other forms of malware.

To prevent the most current viruses, you must update your antivirus software regularly. You can set up most types of antivirus software to update automatically. So no virus will effect your computers.

Like the flu, a virus can slow down the machine and, in some cases, death. So is better to protect themselves to minimize the possible effects of an invasion of viruses. One thing to know against, not because you have an antivirus program that you are 100% protected. You also have to take care while installing some software. I protect my computer and my data by installing antivirus.