Viruses: A virus is basically an executable file which is designed such that first of all it should be able to infect documents, then it has to have the ability to survive by replicating itself and then it should also be able to avoid detection.
Computer viruses can be classified into several different types.
File or program viruses: They infect program files like files with extensions like .EXE, .COM, .BIN, .DRV and .SYS. Some file viruses just replicate while others destroy the program being used at that time. Boot Sector Viruses (MBR or Master Boot Record): Boot sector viruses can be created without much difficulty and infect either the Master boot record of the hard disk or the floppy drive. Polymorphic Viruses: They are the most difficult viruses to detect. They have the ability to mutate this means that they change the viral code known as the signature each time it spreads or infects etc.
Antiviruses: The ideal solution to the threat of viruses is prevention. Do not allow a virus is get into the system in first place. This goal is in general difficult to achieve, although prevention can reduce the no: of successful viral attacks. The next best approach is to be able to do the following.
- Detection, Identification, Removal.
Basic techniques are
Scanners: Scanners are programs that scan the executable objects (files and boot sectors) for the presence of code sequences that are present in the known viruses.
Monitors: The monitoring programs are memory resident programs, which constantly monitor some functions of the operating system.
Integrity Checking: A program, which can detect that the other executable objects have been modified, will be able to detect the infection. Such programs are usually called integrity checkers.
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