What can viruses and other destructive software do to your system?

Best case, a virus may turn out to be a nuisance, such as playing a song repeatedly at random times. In the worst case, a virus can rapidly spread through a system or a group of systems on a computer network, rapidly destroying programs and data. The biggest problems with viruses is that they can spread and do their work silently, quickly, and efficiently, before you ever discover that they are there.