Viruses, worms and Trojan Horses

Viruses, worms and Trojan Horses are all malicious programs that can cause damage to your computer, but there are differences among the three.

Here is the definations of Viruses, worms and Trojan Horses provided for you.

A computer virus:- it is attached to a program, or file so that it is spread from one PC to another computer.

Almost all viruses are attached to an executable file, which means the virus may exist on your computer but it cannot infect your computer unless you run or open the malicious program.

i.e. A virus cannot be spread without a human action, (such as running an infected program).
It is spread generally by sharing infecting files or sending e-mails.


worm :- similar to a virus but it has the capability to travel without any help from a person.
a worm can send a copy of itself to everyone listed in your e-mail address book without your action .
worm consumes too much system memory (or network bandwidth), causing Web servers, network servers and individual computers to stop responding.

Trojan Horse :- it will appear to be useful and legitimate software or legitimate files but will actually do damage once you installed or run on your computer.
They can cause changing your desktop( like adding silly active desktop icons) , deleting files and destroying information on your system.gives malicious users access to your system( called as BACKDOOR)

Note:-Unlike viruses and worms, Trojans do not reproduce by infecting other files.

Note:-A "blended threat" is a sophisticated attack that bundles some of the worst aspects of viruses, worms, Trojan horses and malicious code into one threat.