Virus, The Danger Through Computers

http://www.webroot.com/us/en/home/resources/articles/pc-security/computer-security-threats-computer-viruses

A computer virus is a malware program that, when executed, replicates by inserting copies of itself (possibly modified) into other computer programs, data files, or the boot sector of the hard drive; when this replication succeeds, the affected areas are then said to be "infected"

Clearly writing and spreading virus programs are unethical acts; they have very serious consequences, and cause systems to crash and organizations to cease operating for certain periods. One of the most concerning consequences of such actions is when viruses interrupt the smooth functioning of an organization such as a hospital, which could in extreme cases even cause people to die. Logic bombs are also sometimes planted. There is obviously a lot of anti-virus software on the market now though that helps to deal with this ever-growing problem. 

How To Prevent Computer Virus Infections? 

1. Don't open unknown attachments in emails or do a virus scan after opening them. (If you get an email from a person that contains one or more viruses, the viruses may infect files in the computer. The viruses might also send emails to people from your email address book or email folders automatically)

2.  Download files only from trusted sites. If you download a program or a data file from the Internet or other shared networks, viruses might be transferred to your computer. Sometimes the free software programs on the Internet have viruses especially if you are downloading from sources such as Torrent or Usenet newsgroups.

3. Remember to do a virus scan for them after peripheral devices are connected to your computer. The devices such as MP3 players, USB thumb drives, memory cards or CD drives are also means of spreading viruses.