What is a Stealth virus?

This particular breed of virus attempt to hide from your antivirus program and your operating system, even Vista with its integrated protection feature. Stealth viruses hide inside your memory and prevent your operating system from gaining access. The end result of a stealth virus is a computer that thinks it's clean as a whistle when really, it's inhabited by a covert and cunning virus. These viruses can even trick your system to think it's not consuming memory. Stealth viruses can sometimes go unnoticed for weeks and months.