Difference Between Virus,Worm,Trojan

One common mistake that people make when the topic of a computer virus arises is to refer a worm or Trojan horse as a virus though they are different from each other.All three harms the computers but  have differences and cannot be treated as same.Following gives brief overview of each of them.

What is a Virus?

Virus is a program that attaches itself to a program or a file and spreads from one computer to another computer and leaving infections as it moves.Mostly viruses are attached to an executable files, which means that the virus may exist on your computer but it actually cannot infect your computer unless you run or open the malicious program.Virus cannot be spread without a human action to keep it going. Because a virus is spread by human action people will unknowingly continue the spread of a computer virus by sharing infecting files or sending emails with viruses as attachments in the email.

What is a Worm?

Worm is similar to a virus by 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 human action. A worm takes advantage of file or information transport features on your system, which is what allows it to travel without human interaction.

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 negative effect. As worm replicate itself, it may consumes too much system memory (or network bandwidth), causing Web servers, network servers and individual computers to stop responding.

What is a Trojan Horse?

Trojan Horse is a type of virus which is named after a  Mythological Trojan Horse and it appears to be legitimate software to the user at first glance but will actually do damage once installed or run on your computer.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. Unlike viruses and worms, Trojans do not reproduce by infecting other files nor do they self-replicate.