Viruses, Worms and Trojans (Oh My!)
by: Debbie Jacobsen
Anyone who uses a computer has undoubtedly heard the terms "computer virus", "worm", and "Trojan". Most use these terms interchangeably to describe a virus. What you may not realize though, is that computer worms and Trojan horses are not computer viruses at all.
While each of these three computer security threats shares some common characteristics, there are some distinct differences between viruses, worms, and Trojans that cause them to stand on their own as a category of malicious software. The main similarity is that all are bad, and can potentially cause you, your computer, or your network a great deal of harm.
Common Characteristics of Viruses, Worms, and Trojans
All computer viruses, worms, and Trojan horses are considered to be "malware", also commonly referred to as malicious software. Spyware and adware also fall into the category of malware, as is any other type of software that is designed to perform malicious and/or unwanted activity.
Viruses, worms, and Trojans have been around for awhile, and are often packaged together (i.e. a virus that launches a worm when executed, a worm that plants a Trojan, etc...). Because of their longstanding use as a means of performing disruptive and destructive tasks, anti virus software developers include protection against Trojans and worms in their antivirus applications.
Anti virus software (if updated regularly) will help protect you from all three dangers.
Differences Between Computer Viruses, Worms, and Trojan Horses
A Computer Virus is attached to a program or file, and is designed to spread from one computer to another. It infects the computer it is installed on, and is usually spreads when the infected file (usually an .exe file) is shared with others via email, disk, USB drive, or CD. A virus has to have human action in order to launch and deliver its "payload".
The file that the virus is attached to cannot open itself; a user has to open it in order to execute the virus. Viruses have many symptoms, depending on the intent. Computer viruses can erase or corrupt files and applications, crash your system by making so many copies of files that the hard drive fills up, or make a computer inoperable by altering critical system files.
A Computer Worm is like a virus in that it is also attached to a file, and the file has to be opened before infection can take place. Unlike a virus, that is passed from computer to computer via user action (usually unintentional); worms are designed to self-replicate and spread without any effort on the user's part. When you open a file that contains a worm, it starts spreading through networks and emails immediately. The main purpose of a worm attack is to bring down systems and networks by consuming great amounts of bandwidth and memory.
Worms are also used as a means for a remote attacker to tunnel into your system. Many worms will replicate themselves by sending "clones" to everyone in your email address book. These emails are sent out immediately upon opening the infected file, and may not show up in your "sent items" folder.
A Trojan Horse is also included in a file, and like a virus, does not propagate itself. Trojans are tricky, in that they are often disguised as some type of useful or interesting software. When the software is installed (Trojans are normally embedded in .exe files), the Trojan is activated, and sometimes you don't even realize its there.
Trojans can do many things, and while some are designed to be dangerous, others are just annoying. A Trojan might destroy certain types of files, alter critical system files, change your desktop icons, or simply plant a "backdoor" on your system that can be used by a hacker or cyber criminal at a later date. Trojans are usually passed from PC to PC by email or disk file transfer, because the sender doesn't know that the file carries a harmful Trojan.
Protection from Viruses, Worms, and Trojans
The good news is that Antivirus software will provide a great deal of protection against known computer viruses as well as worms and Trojan horses. The bad news is that antivirus software won't necessarily provide total protection. You still need a good firewall to keep cyber criminals out, and you need anti spyware to protect against the other types of malware that antivirus software isn't so good at catching. For the absolute best protection, use a Computer Security Suite.
Be sure to get the most recent updates for your operating system and all applications installed on your PC. This is especially important for Windows users, as the majority of malware is designed to work on the world's most popular operating system. Updates will patch newly discovered "security holes" and will help prevent many viruses, worms and Trojans from completing their "mission".
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