Computer viruses spread via emails and email attachments and through memory sticks. They are small program that spread from one computer to another. They modify or destroy any data and distrupt normal operation of the operating system.
Most common forms of malware are Spyware, Adware, Trojan Horses,
and Worms.They can destroy or steal your data without your knowledge.
Spyware – These collect user data/information and details on the operation of computers without the knowledge of the user. They inject code into your browser or run programs at boot time. Once run they can do any damage to your computer.
Adware – These display advertisements on your computer by installing itself on a computer
without a user’s permission. Adware track internet usage data and habits of the user to deliver advertiesments.
Trojan Horses – These viruses cannot self-activate. They are harmful programs that
disguise themselves as useful at first, but will collect personal data in the background and
wait for an exact date or time to begin harming the computer. Consider it as a time bomb in your computer.
Worms – These viruses do not need human interaction to spread from one computer to another. They have the ability to self-activate within a computer. For example, It will open your mail client, make copies of itself and send emails to all people in your address book. This will repeat in computers of the recipients. They spread automatically at a rapid rate within a computer network.
Most email viruses are disguised as photos, audio and video animations etc Users need to be very extra careful when opening any email with an attachment
Its possible for you to download them from internet thinking that they are harmless software tools.