Types of Viruses

The Trojan virus gets its name from an incident that occurs in Homer's Iliad. Similar to how the Greeks in Homer's poem sent an army of men, hidden in a wooden horse, to the Trojans to get into the wall of the city. A Trojan horse appears to be nothing more than an interesting computer program or file, such as "saxophone.wav file" on the computer of user who's interested in collecting sound samples. The Trojan virus once on your computer, doesn't reproduce, but instead makes your computer susceptible to malicious intruders by allowing them to access and read your files. Making this type of virus extremely dangerous to your computer's security and your personal privacy. Therefore, you should avoid downloading programs or files from sites if you're not 100 percent positive of what the file or program does.
A Worm is a virus program that copies and multiplies itself by using computer networks and security flaws. Worms are more complex than Trojan viruses, and usually attack multi-user systems such as Unix environments and can spread over corporate networks via the circulation of emails. Once multiplied, the copied worms scan the network for further loopholes and flaws in the network. A classic example of a worm is the ILOVEYOU virus.
The best way you can protect yourself from worms is by updating your security patches. Operating systems and application vendors normally provide these patches. In addition, you should avoid opening email attachments from unknown senders.

Email viruses use email messages to spread. An email virus can automatically forward itself to thousands of people, depending on whose email address it attacks. To avoid receiving virus-laden emails, always check that your antivirus software is up-to-date and also stay clear of opening attachments, even from friends that you weren't expecting or don't know anything about.