Stealth virus.

Stealth virus is a hard one for detecting and disposing as they intercept operating system's requests for infected files or disk sectors and replaces them with uninfected disk sectors. Stealth virus is also known as invisible virus. During the testing of operating system and computer's memory antivirus program reads data files and system sectors of hard and floppy disks by means of operating and basic insert-outsert systems. Some viruses leave at the computer's short-term memory special modules after launching. Those modules intercept programs' referring for disk cache. The module replaces the infected file or sector that was requested by any program with uninfected disk sectors. So, stealth virus tricks antivirus program and remains unnoticed.

As we said before viruses are created by the same human who creates antivirus programs and as so there weren't and, I hope, won't such virus which is impossible to be detected and disposed. There's a simple way to deal even with problem of stealth virus. All you have to do is just deactivate stealth's mechanism of disguise. Operation of deactivating is rather simple; you have to load your computer's system from uninfected floppy disk and right after that activate antivirus system testing before you run any other program, which may also be infected. In conditions of floppy disk system loading there's no chance for virus to set residential module at short-term memory of computer, and as so activate disguising mechanism. Now antivirus program is able to read real data of hard disk and detect stealth virus.

Most of antivirus programs confront stealth virus's efforts to remain invisible. Still, in order to provide your antivirus with hundred per cent success you should run the operating system from uninfected floppy. Otherwise there's a chance for virus to hide itself and then a great damage for your computer will be caused. System floppy disk should be ready-made beforehand; it should contain both system files and antivirus software.

Some kinds of antivirus programs are being so successful in confronting to virus's efforts remain invisible that they are able to detect virus as it attempts to disguise itself. These programs use different methods of reading the system information and in case if results of two or more methods mismatch they informs you about infecting of stealth virus.