Virus
A computer virus is a computer program that can copy itself and are designed to from one computer to another and to interfere with computer operation. Once entered into your computer, it can corrupt or delete data, use your email account to spread itself to other computers, degrade your computer performance-lower its speed for example-by using your computer’s memory, disk space or even erase everything in your hard disk. There are 4 types of virus: Boot sector computer virus, Master Boot Record (MBR) computer virus, File infector computer virus, Macro computer virus and Multi-partite computer virus. (Wikipedia, Microsoft, techFAQ)
A virus can only spread from one computer to another when its host is taken to the uninfected computer via a network, Internet or a removable device. However, viruses can easily spread by attachments in e-mail messages, instant messaging messages, funny images, greeting cards,…They can also be hidden in illicit software or other files or programs that you might download. (Microsoft)
To stop viruses, you can use a tool called System Restore, which restores the registry and critical system files to a previous checkpoint, or reinstall the operating system.(Wikipedia)
To prevent your computer from being infected by viruses, it's essential to keep your computer current with the latest updates and antivirus tools, stay informed about recent threats, and to follow a few basic rules of safety when you surf the Internet, download files, and open attachments. Always remember not to open an attachment file unless you know who it’s from and what it’s for. (Microsoft)
“Computer virus - Wikipedia, the free encyclopedia.” 4 Dec 2008 .
“Computer Viruses: What is a Computer Virus? | Microsoft Security;.” 4 Dec 2008 .
“HowStuffWorks "How Computer Viruses Work".” 4 Dec 2008 .
“What is a computer virus?.” 4 Dec 2008 .
Trojan horse
Trojan horse is a malicious program that is disguised as or embedded within software that appears...