We generally consider everything that is detected by an antivirus as virus, but this is not the case.The antivirus not only provides protection against viruses but it also protects us from Trojans, Worms and Spywares. All these can be harmful to your computer hardware and software. Today I will differentiate all these terms from each other.
1.Virus: A virus is a self replicating program that attaches itself to an executable file. When the file is executed the virus automatically gets executed and enters into system memory. Once it enters into system memory it either searches for other files that can be infected or stays in the background and infects the files that uses the virus infected program.
2.Worms: Worms are very similar to viruses but differ in the way that they do not bind themselves to the executable files, instead to replicate themselves they use the network. If you find excessive use of your network bandwidth then you may be infected by a Worm. So, a Worm does not require a user to execute any file, for its execution it can work without user intervention.
3.Trojan Horse: A Trojan Horse is a harmful program which may seem harmless to the user before its installation, but instead it is programmed or reverse engineered to facilitate unauthorized remote access to the computer. Trojans do not replicate themselves.
4.Spyware: A Spyware is a program that secretly monitors and collects pieces of information. They usually run in stealth mode and cannot be detected easily. Keyloggers are great examples of Spyware softwares. There are not limited to just spying, but can also send data to remote computers.
Now here I'm providing you the list of most harmful Viruses and Worms in the history of computers:
Storm Worm
Leap-A/Oompa- A
Sasser and Netsky
MyDome (Novarg)
SQL Slammer / Sapphire
Nimda
Code Red and Code Red II
The Klez
ILOVEYOU
Melissa