Computers are very detailed machines that function by set rules, codes and languages. Everything follows a pattern and schedule in order to operate efficiently. Computer viruses can affect the cosmetics of a computer such as the screen and display appearances or the simple functions such as the way the keyboard operates or the functionality of the drives. Some of these symptoms may seem to be only a minor inconvenience, but when you see these signs you should wonder what may have caused the change and what else may be going on that you can't see. Other symptoms can include loss of files, decrease in memory space, slow operation and damaged programs.

The writer of the virus determines how they will infect the system as well as what they want the virus to do. In most cases, a virus will perform damage to the host system, and may do this while performing another function such as retrieving information, and then spread to the remainder of the network.

A computer virus is similar to a medical virus in that it often occurs even when precautions were taken to prevent it. Particularly malicious viruses steal information and data, which may be confidential. This may be customer or client information of a personal nature whether medical, financial or some other form. It may be company information specific to employee's records, user names and passwords or other functions of the business. Information may simultaneously be erased. It can pick up information from any other computer in the network. It can locate other users and obtain their information.

There are many programs available and they are a must-have for an individual's personal computer and certainly for that of a business. Strong measures must be taken to prevent viruses within a company, as one infected computer is opening the door to the entire network, putting clients, customers and even employees at risk. Businesses should understand that the condition of their system is susceptible to change with every employee that signs into the network. Training should be instituted to prevent damage by teaching employees how to determine what is safe use of the system, how to update their protection programs and how to know if something is questionable and when to bring it to the attention of the IT department. It is always helpful to set up the virus protection programs to run automatically and the individual systems or the network as a whole can be set to automatically update the programs that are install along with fixes and patches as needed. In addition to anti-virus programs a filter may also help to block viruses.

While the anti-virus is placed inside the firewall, a filter is placed on the outside and closer to the server. Users may be limited as far as what can be received and may not be able to open attachments. This will undoubtedly create an inconvenience, though it is in the best interest of the company and will save money by eliminating loss of business if a shutdown is needed to correct a problem. A virus usually spreads very quickly and for a large company this can be costly. Prevention is always the least costly way to reduce the risk of virus.