If computer programs are starting up automatically or unexpectedly closing, this can be a sign of a computer virus. Another sign is a computer running slower than normal.
One of the most common symptoms of a computer virus is the computer shutting down of its own accord, opening or closing programs suddenly, and displaying unexpected messages. Many viruses are programmed to cause damage to the Windows operating system and installed programs, which is why unexpected shutdown behavior is a common sign.
Slow performance is another sign of a computer virus, but this can also be caused by low memory, the presence of spyware and adware, or a hard disk that needs to be defragmented.
Other signs that a computer is infected with a virus are an overworked hard drive and extensive broadband activity. Some viruses work by sending multiple copies of messages to email contacts, which overworks the modem and causes the activity light to remain constantly lit. If the hard disk on the computer is continually making sounds, this is another sign of a potential computer virus.