Viruses

I know that a virus infects your computer and can cause it to fail, but that's all I really know. Viruses are very  dangerous and can be protected by antivirus software.
Questions?
How do you get a virus?
If you get a virus can you get rid of it after your computer is infected?
Is sending a virus illegal?
Links
http://support.microsoft.com/kb/129972
http://www.us-cert.gov/reading_room/virus.html
http://www.nampa.net/download/Virus/VirusLegal.php
http://www.infoniac.com/uimg/virus-alert-sign.jpg
Info

• Viruses corrupt and delete data on your computer
• Viruses usually come from attachments on emails
• Viruses can be disguised as anything; pictures, videos, audio, or a download
• A virus can come as a Trojan horse or worm. Trojan Horse- a computer program that is hiding a virus. Worm- a virus that can be received and spread without people starting it.
• Viruses first infect the computer then copy itself again and again.
• In the U.S. it is illegal to make a virus, but in most countries it is not illegal. However it is illegal to spread a virus in most countries.
• You can stop a virus by using antivirus software and updating it frequently.
• There are software's called rogue security software that can be viruses or make you think you have a virus to make you pay more to get rid of it.

Relation
Viruses can ruin my computer. My dad always makes sure nothing happens and keeps the antivirus software updated and managed. I have yet to have a virus, and plan on keeping it that way.
Last Question?
How can people create a virus and disguise it?