Computer viruses are very risky and can damage all the data files that you have on your pc and the pc itself. There are many types of them. It injects copies of itself into other programs on your computer system. They do damage the executable programs and the system files! Or display annoying messages and popups on your screen and send infected junk emails to people from your email address.
You can notice easily if your Computer is infected throughout sending anonymous emails to friends, some programs crash suddenly and the PC will tilt, also if the computer fails to start or even more if there's weird popups appear every time on your screen.
Whenever you share documents with another computers throughout chatting rooms or from people that you don't know, swapping files from an infected disks or surfing the internet into unsecured websites and downloading files from these anonymous websites or FTP sites and opening attachments from unknown emails, YOU ARE IN A BIG RISK! And these files are in .EXE or .VBS or .COM or .BAT or .PIF formats you should be aware.
There are different types of viruses:
-Worm: make copy of itself, take control of the pc and your email and email themselves.
-Macro virus: Infects data files, word and excel rely on pseudo programming code.
-Trojan Horse: the virus in disguise usually they use the hackers
(Like the "subseven" & "NetBus" hacking program to take control of the hole PC.)
Script virus: are written in one of the script languages Java, ActiveX, or VBScript used form web pages and to create emails are activated when the script runs.
To protect yourself from viruses you shouldn't open files from people that you don't know in chat rooms, newsgroups or unreliable websites. USE ANTIVIRUS PROGRAMS it's essential or else your pc will be in danger. Use the MCAFEE antivirus it's one of the bests and many others like norton antivirus or PC cillin and always update the virus definitions!!!