Sometime the term computer virus is used to describe a logic bomb in which a piece of unauthorized code acts as a parasite that attaches it self to a host program during a copy operation. Like their biological counterparts computer viruses reproduced and spread; copy commands embedded in the virus code to make, it reproduce and transmit commands may be inserted to spread the virus from one computer to the other on its network. Unfortunately, viruses are common in today’s, computer system and the potential problems they may cause must be addressed. In 1992, the potential problems became even worse. Professional computer viruses fighters were outraged by the publication of the book that contain the source code heeded to create potentially destructive viruses, plus coupons for floppy disk containing executable virus program.
To be able to analyze and remove viruses from the computer system you need to ascertain its type some of the types have been discussed below:
Boot Sector Viruses
Macro virus is the first virus to infect the data files, rather than executable. Macro viruses infects the files in the form of macro or OLE objects and are easier to write than “traditional” files viruses which are mostly written in assembly code. Today many applications have macro languages, so the problem is a growing one. Macro viruses spread by people sending infected files to each other, entirely innocently, either on floppy disk, or via the internet LAN, or via an external e-mail system.
Many applications provide the functionality to create macros. A macro is a series of commands to perform some application specific task. Macros are designed to make, life easier like automating some everyday tasks, for instance, doing calculations. Macros can be saved as a series of keystrokes; or they can be written in some macros languages.
Some viruses are badly written and “lose” their own macros. The original virus may consist of the set (Auto Open, File Save, and File Save As), if the replicates via Auto Open, the complete macro set will be preserved. However, if the user invokes File (Save As), the virus will fail to copy the File Save macro. The resulting virus set (Auto Open, File. Save As) is known as developed Macro and original virus is developing.
Boot Sector Viruses:
Once of the most common kind of viruses are boot sector viruses, for example. Form and Stoned. These viruses infected the floppy disks in either of the following parts:
Master Boot Record (MBR)
Partition Sector of the DOS Boot Record (DBR)
DOS Boot sector of hard disks
The following examples shows how a boot sector virus spreads: you have got a floppy disk with data on it, perhaps some page maker file. This is part of a project that you are doing jointly with a classmate. What your classmate does not know is that his computer is infected with a boot sector virus and therefore, so is the disk that has been sent to you. You put the disk in drive A: and start using these files. So far, the virus has not done anything. But when you finish for the day, you switch off the computer and go home. The next day, you come and switch on. The floppy disk is still in drive A. so the computer is trying to boot up from there. It loads the first sector into memory and executes it, or if it cannot find DOS on the disk, tells you: “Not a system disk, please press any key to continue”. Everyone has seen this message numerous times.