A stealth virus is a file virus. It infects the computer and then hides itself from detection by antivirus software. It uses various mechanisms to avoid detection by antivirus software. It hides itself in computer memory after infecting the computer. It also masks itself from applications or utilities. It uses various tricks to appear that the computer has not lost any memory and the file size has not been changed. The virus may save a copy of original and uninfected data. When the anti-virus program tries to check the files that have been affected, the virus shows only the uninfected data. This virus generally infects .COM and .EXE files.