COMPUTER THREATS Computers are susceptible to threats (as does every good thing) in form of viruses i.e. unwanted or malicious programs create by some programmers to infect other computer programs by modifying them or completely corrupting them, therefore rendering them useless for the computer owners.The reason for this malicious act by this virus programmers, is not really known, may be to pave a way for anti-virus program or software market. For more visits http://computersworld.synthasite.com Computer threats are critically analyzed bellow. VIRUSES A computer virus as defined by Dr Fred Cohen, is a program that can” infect” other programs by modifying them to include a possibly evolved copy of it. A computer virus is one kind of a threat to the security and integrity of a computer system. Like other threats, a computer virus can cause the loss or alteration of programs or data and can compromise their confidentiality. Unlike many other threats, a computer virus can spread from program to program, and from system to system without direct human intervention. We also have Trojans worms and logic bombs which are also malicious programs. The essential component of a virus is the set of instruction which when executed spreads itself to other previously uninfected programs or files. A typical computer virus performs two functions or rather has two parts. The first part is the self-replicating code which copies itself into previously uninfected programs or files. The second is the payload which executes whatever other instruction the virus author included in it, this of course depends on the motive of the virus author. These instructions can do anything ranging from displaying a message or erasing files or subtly altering stored data. In some cases, a virus may contain no intentionally harmful or disruptive instructions at all. Instead, it may cause damages by replicating itself and taking up scares resources such as disk space, RAM space, and CPU time or network connection. Most viruses were written in order to prevent software piracy though, some were written by some programmers in order to propagate their malicious activities and hence, these virus programs end up infecting a large community of computer users and eventually causing great damage to systems. For more visits http://computersworld.synthasite.com WHAT ARE VIRUSES Generally, virus programs are unwanted programs which affect the internal working of our computers (systems). We have various types of unwanted programs which have been classed as Worms, Trojans, and Logic Bombs and Viruses. The basic difference in these malicious programs is in the characteristic way of their behaviour. In general however, they have been classed as viruses since they are all unwanted programs which have the capacity to destroy or alter the normal way a computer system works. VIRUS TYPES BY POINT OF ATTACK Basically, viruses are classed according to their characteristic behaviour. Viruses can therefore, be divided into four categories according to the executable items which they infect. They include: i. Parasitic Viruses Parasitic viruses modify the content of .COM and/or EXE files. They usually insert themselves at the end or at the beginning of the file. Leaving the bulk of program intact. The initial jump instruction in the program is modified but program functionality is usually preserved although, there are several viruses that overwrite the first few hundred bytes of the program rendering it useable. When an infected program runs, the virus code is executed first, the virus then returns control to the original program which executes normally. The extra execution time due to the virus is normally not perceptible to the user. ii. Boot Sector Virus Boot sector viruses modify the content of either the master boot sector or the DOS boot sector depending on the virus and the type of disk. These viruses usually replace the legitimate content of any disk’s boot sector with their own version. The original version of the Boot sector is normally stored somewhere else on the disk (the Boot sector is an area on the disk which contains information that is loaded into the computer’s memory when you start the system) so that on bootstrapping the virus version will be executed first. They are usually 512 bytes in size. iii. Multi-partite viruses A comparative recent development has being the emergence of viruses which exhibit the infective characteristics of sector viruses and parasitic viruses. For example, the flip virus infects executable files (both .COM and .EXE) as well as the master both sector of hard drives floppy disks. iv. Companion viruses Companion viruses exploit the Dos property that, given two programs with the same name but different extensions, the Operating system will execute a .COM file for every .EXE file it “infects”. The .COM file is usually marked “hidden” and contains the virus code which also executes the .EXE file. Companion viruses do not spread widely in practice; since the DOS copy command does not copy “hidden” files. Some examples of these computer viruses include: Jerusalem Virus, Palestine Virus, Eddie Ii Virus, Data Crime Virus, Aids Ii Virus,V2100 Virus, Stoned Virus, Saturday Virus, Israeli Virus, D2 Virus, Tequila Virus, Antiexe Virus etc we have over 10,000 viruses. For more visits http://computersworld.synthasite.com)