Definitions for "Stealth virus"
A virus that hides itself in the boot sector so it remains undetected, making it difficult to disinfect. It has the ability to alter data to hide the virus by intercepting the boot sector.
Stealth Virus hides its presence by making an infected file not appear infected, but doesn't usually stand up to anti-virus software. Many stealth viruses intercept disk-access requests, so when an anti-virus application tries to read files or boot sectors to find the virus, the virus feeds the program a "clean" image of the requested item. Other viruses hide the actual size of an infected file and display the size of the file before infection.
Viruses that go to some length to conceal their presence from programs which might notice.