FAQ Hero
Vulnerability Management

What is the difference
between viruses, worms
and trojan horses?

What is the Difference Between Viruses, Worms, and Trojan Horses?

The most common misconception about Computer Viruses is that they’re the same thing as a Computer Worm or Trojan Horse. While the words Trojan, Worm and Virus are often used interchangeably, they are not the same. Viruses, Worms and Trojan Horses are all malicious programs that can cause damage to your computer, but there are differences among the three, and knowing those differences can help you to better protect your computer from their damaging effects.

What is a Computer Virus?

A Computer Virus is a type of computer program that attaches itself to other programs or files when executed and writes its own code so it can spread from one program to another, leaving infections as it travels. Much like human viruses, Computer Viruses can range in severity: some viruses cause only mildly annoying effects while others can damage your hardware, software or files. Almost all Computer Viruses are attached to an executable file, which means the virus may exist on your computer, but it cannot infect your computer unless you click on, run or open the malicious program. It is important to note that a virus cannot be spread without social engineering and a human action, such as clicking on a bad link or running an infected program to keep it going. People continue the spread of a computer virus, mostly unknowingly, by sharing infected files or sending emails with viruses as attachments in the email.

What is a Computer Worm?

A Worm is like a Computer Virus by its design but is a sub-class of a Virus or Trojan Horse. Worms spread from computer to computer, but unlike a virus, it has the capability to travel without attaching to a host program and can run independently. A Worm takes advantage of file or information transport features on your system, which allows it to travel unaided. Worms typically spread through the internet or through your LAN (Local Area Network) connection. 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 email 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 down the line. Due to the copying nature of a worm and its capability to travel across networks the result in most cases is that the worm consumes too much system memory (or network bandwidth), causing web servers, network servers and individual computers to stop responding. In the much-talked-about Blaster Worm event, the worm was designed to tunnel into your system and allow malicious users to control your computer remotely.

What is a Trojan Horse?

A Trojan Horse is any type of malware that misleads users of its intent, like a destructive program that appears as a genuine application or software program. Trojan Horses are named after the Ancient Greek story of the deceptive Trojan Horse that took down the city of Troy. Unlike viruses, Trojan Horses do not replicate themselves, but they can be just as destructive. Trojans also open a backdoor entry to your computer, giving command to malicious actor or allowing malicious users/programs access to your system. This leads to confidential and personal information being stolen.