What are Viruses? Viruses come in all different forms and sizes. True viruses are small computer programs that attach themselves to programs in your computer - such as Microsoft Word or Office. When your programs are run, so is the virus. Although most viruses are harmless, some can erase or change important files in your computer. Remember the story of the Trojan horse? It was a wooden horse that was built to gain access to a city. It was not ordinary horse. It secretly held an entire army of Trojan soldiers. The Trojan virus is very similar. These computer programs sneak into your computer by riding along with real programs. Once it's in, it is often used to let another person get into your computer without you knowing. Worms are programs that run all by themselves. They don't need to attach to other programs. They spread within your system and reproduce until it clogs up your system. Worms are most harmful to network systems. Macros are programs that attach to application programs such as Microsoft Word or Excel. There are good macros that let you do useful things in these programs. Bad macros are called macro viruses and can infect and damage files. Once you open a file with a macro virus, it can infect every file you open in that application. The I Love You virus was a combination between a macro virus and a worm. It reproduced itself across the network. Then through Microsoft Outlook sent the virus to everyone in the address book. …and how do they get in your computer? We often get computer viruses through e-mail. Viruses do NOT spread by the text of an e-mail message, but rather by attachments to that e-mail. Once an attachment is opened, the virus is let loose to reek havoc! So it's not opening an e-mail, but opening an attachment that can be dangerous.