If you have any suspicious about viruses on your computer you need to use an updated Antivirus program to search and remove viruses.
In case of Windows 8 and 8.1, the antivirus application is already installed and ruining in the background. Usually, if viruses are detected you are noticed. In case of older operating systems like Windows 7, Vista or XP, you need to manually install an antivirus software.
Therefore… to scan for viruses you need to: