Computer viruses are a major problem for computer users around the world. These are programs capable of replicating and infecting your system. In addition to being able to reproduce, viruses can be designed to perform different destructive actions, so a virus can destroy programs and data immediately or remain inactive for a while and cause damage within a while . Therefore, learning about viruses can help you keep your system virus-free. Computer viruses are becoming more sophisticated and are transferred between computer systems using a variety of methods. Although email is the primary means of spreading these recent computer viruses, it is not the only way. A computer virus can also enter a network through CDs, floppy disks, Internet downloads, file sharing programs, or by remote users connected to a network with an infected system. Once a computer virus enters a network, it can easily spread from one computer to another. Once viruses have infected your system, they can wait for a signal before damaging the system: time-triggered actions and logical actions. Time-based actions are signals activated by a specific time or date. Logical actions are activated when specific functions are executed. Most computer viruses have three basic characteristics: a replication process, an activation process, and a goal. The replication mechanism searches for other programs to damage, if it finds any, it inserts the hidden instruction into the program and then it modifies the execution sequence of the program. The activation mechanism checks for the occurrence of an event. When the event occurs, the computer virus executes its goal. Computer viruses have affected a significant number of computers in recent years. There is... middle of paper ...... a firewall to protect your system's network, so that viruses that spread through email are prevented from entering the network.4. All emails should first be filtered and scanned to avoid surprise attacks, and emails with certain attachments such as .EXE, .COM, and .SCR should always be prevented from entering the network or the system.5. All users who work in a business or at home should be informed and should clearly understand how to avoid email viruses sent from an unknown source. Therefore, caution should be exercised when opening attachments.6. Always scan Internet downloads; although the files may look clean, you still need to take percussion in order to prevent viruses from entering your system easily. And this analysis must be performed somewhere on the network where the virus has no chance of spreading through the network..