Computer viruses are small software programs that are designed to spread from one computer to another and to interfere with computer operation. A virus might corrupt or delete data and files on your computer, use your e-mail program to spread itself to other computers through your email list, or even erase everything on your hard drive causing you to lose everything.
Viruses are most easily spread by attachments in e-mail messages or instant messaging messages. That is why it is essential that you never open e-mail attachments unless you know who it's from and you are expecting it. All the software programs we recommend above automatically search emails for viruses. Viruses can be disguised as attachments of images, greeting cards, or even audio and video files. Viruses also spread through downloads on the Internet. They can be hidden in illicit software or other files or programs you might download.
To help avoid viruses, it's essential that you keep your computer current with the best anti-virus software program that offers the latest updates and antivirus tools. It's important that you stay informed about recent threats, and that you follow a few basic rules when you surf the Internet, download files, and open attachments. Once a virus is on your computer, its type or the method it used to get there is not as important as removing it and preventing further infection.
Computer Trojans Horses - The term comes from Greek mythology about the Trojan War, as told in the Aeneid by Virgil and mentioned in the Odyssey by Homer. According to legend, the Greeks presented the citizens of Troy with a large wooden horse in which they had secretly hidden their warriors. During the night, the warriors emerged from the wooden horse and overran the city.
A Trojan horse is full of as much trickery as the mythological Trojan Horse it was named after. The Trojan horse, at first glance will appear to be useful software but will actually do damage once installed or run on your computer. Those on the receiving end of a Trojan horse are usually tricked into opening them because they appear to be receiving legitimate software or files from a legitimate source. When a Trojan is activated on your computer, the results can vary.
Some Trojans are designed to be more annoying than malicious (like changing your desktop, adding silly active desktop icons) or they can cause serious damage by deleting files and destroying information on your system. Trojans are also known to create a on your computer that gives malicious users access to your system, possibly allowing confidential or personal information to be compromised. Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate.
Computer Worms - A worm is similar to a virus by its design, and is considered to be a sub-class of a virus. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without any help from a person. A worm takes advantage of files or information transport features on your system, which allows it to travel unaided. The biggest danger with a worm is its capability to replicate itself on your system, so rather than your computer sending out a single worm, it could send out hundreds or thousands of copies of itself, creating a huge devastating effect.
One example would be for a worm to send a copy of itself to everyone listed in your e-mail address book. Then, the worm replicates and sends itself out to everyone listed in each of the receiver's address book, and the manifest continues on down the line. Due to the copying nature of a worm and its capability to travel across networks the end result in most cases is that the worm consumes too much system memory, causing Web servers, network servers and individual computers to stop responding.
Rootkits - are not destructive software programs like viruses, but they are designed to conceal the presence of malicious programs on a computer while other programs are running. Root kits are similar to viruses in the way they modify the code of the software installed on the computer. Both root kits and viruses insert additional code which is meant to hide the infection and keep the system administrator and users in the dark.
However, root-kits are there for one reason only, to ensure that an intruder can access the system and take control whenever they wish, much like a backdoor Trojan horse. Root kits have coded user/password backdoors that allow the intruder access to the system. Unlike viruses, they are limited to allowing the intruder access and they do not need to propagate on the entire system. This is a key point and an important step in learning how to defeat a root kit. In other words, root-kits enable someone to disable or use your computer, or steal information from it, without detection by your defenses to guard privacy and security. So, unless your antivirus or antispyware is combined with anti-rootkit technology, you will be informed your system is clear, when, in fact, you could be infected.
Spyware - Spyware is Internet jargon for Advertising Supported software (Adware). It is a way for shareware authors to make money from a product, other than by selling it to the users. There are several large media companies that offer them to place banner ads in their products in exchange for a portion of the revenue from banner sales. This way, you don't have to pay for the software and the developers are still getting paid. If you find the banners annoying, there is usually an option to remove them, by paying the regular licensing fee.
There are also many PC surveillance tools that allow a user to monitor all kinds of activity on a computer, ranging from keystroke capture, snapshots, email logging, chat logging and just about everything else. These tools are often designed for parents, businesses and similar environments, but can be easily abused if they are installed on your computer without your knowledge. These tools are perfectly legal in most places, but, just like an ordinary tape recorder, if they are abused, they can seriously violate your privacy.