• A computer virus is a program or piece of code that is loaded onto your computer without your knowledge and works against your wishes. They have the ability to replicate to the point of using all available memory, slowing down the machine or crashing the system. All computer viruses are man-made. An even more dangerous type of virus is one that can transmit across networks and bypass security systems. Type of Virus • Virus that infects files This type of computer virus inserts its malicious code into a system's executable files. When the infected file is opened, the virus may overwrite the file and cause damage to the contents of the overwritten file. This type of virus targets a wide range of operating systems • Armored VirusA type of virus designed to thwart analysts' attempts to examine its code by using various methods to make tracing, disassembly, and reverse engineering more difficult. An armored virus can also protect itself from antivirus programs, making it more difficult to track. To do this, Armored Virus tries to trick the antivirus program into thinking that its location is different from the system's real location. • Macro virusA type of computer virus encoded as a macro embedded in a document. Many applications, such as Microsoft Word and Excel, support powerful macro languages. These applications allow you to embed a macro in a document and run it every time the document is opened. By some estimates, 75% of all viruses today are macro viruses. Once a macro virus enters your computer, it can embed itself in all future documents you create with the application• RetrovirusA computer retrovirus is a virus that activates...... middle of paper...... Firewalls can easily be implemented in either hardware or software, or both. Firewalls are often used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. It acts like a security guard at the door that checks all messages entering or leaving the intranet, examines each message and blocks those that do not meet the specified security criteria.“”A firewall protects computers on the network from an intrusion of third parties which could compromise confidentiality. This could be either a hardware program or a software program running on a secure computer. It has two network interfaces; one for the network is to be protected and the other to which it is exposed. A firewall sits between the two networks, a private network and a public network such as the Internet. Restrict access to any spread or harm that may be caused.