Computer viruses can slow and damage computer systems by replicating and spreading inside programs and files. They are difficult to detect and remove because they can spread across entire networks of connected computers. It is important to use antivirus software and seek help from online or offline computer support services that can properly diagnose, remove viruses, and repair any damage caused by infections. Online virus removal services allow remote access to identify and remove viruses quickly and conveniently without needing to send the physical computer away.