The old-fashioned way, through an infected disk, is the most common. Most often, diskettes brought to the office from home are responsible for introducing a virus into a corporate network-computing environment. Most at-risk servers on a network have software that detects incoming viruses, but infections do occur in networked environments, making the rapid spread of a virus a serious risk. With networking, enterprise computing, and inter-organizational communications on the increase, infection during telecommunications and networking is on the rise. You can acquire viruses while downloading software from the Internet or from an electronic bulletin board service.
Viruses can also replicate themselves via e-mail attachments.
The most common viruses are without any symptoms, so anti-virus software is necessary to identify infections. However, many viruses are flawed and provide tip-offs to their infection. Below is a list of indicators that your computer may be infected. These symptoms can be the result of a problem other than a virus. Changes in the length of programs.