The procedure for working of the viruses can be explained in the following steps:
1. A virus may be activated in a computer as soon as a file infected by that virus is run or when an infected file is opened.
2. The virus may cause the first few instructions of a program to jump into the destination of virus source code and consequently the virus code starts executing.
3. The activated virus code gains control over the system.
4. The viruses tend to infect newer files and storages spaces.
Just like there are several viruses causing a variety of diseases in humans, computer viruses are also huge in number and can be classified according to their function and nature. They are described below along with some other malicious programs of similar type:
• Resident Viruses: These viruses permanently reside in the RAM memory and affect the operation of the systems.
• Multipartite Viruses: They spread through infected media and remain in the memory of the system.
• Direct Action Viruses: These viruses infect the files present in the directories of AUTOEXEC.BAT file paths.
• Overwrite Viruses: They cause partial or whole loss of data from files once they affect them.
• Boot Viruses: These viruses infect the floppy disks and drives where information related to booting of devices is stored.
• Macro Virus: The sources of these viruses are programs or applications using macro.
• Directory Virus: They change the directory or path indicating a file location. It makes locating the original files impossible.
• Polymorphic Virus: These viruses encode themselves in a different way so that the anti-virus software cannot detect their presence using string or signature searches.
• File Infectors: They infect programs and files with .COM and .EXE extensions. These viruses can be further classified according to the functions they perform.
• FAT: FAT or File Allocation Table is used for the communication of information and is an important part of the computer.
• Worms: These are similar to viruses and capable of self-replicating. They can be removed from the system using anti-virus software.
• Trojans: Most of us are familiar with Trojans. These malicious codes do not replicate or reproduce on their own.
• Stealth Viruses: These viruses try to trick the antivirus software so that their presence cannot be determined by these software.
• Companion Viruses: These need the accompaniment of the other viruses for execution. In other words, they require the execution of other malicious programs in order to affect the system.
With the presence of so many viruses it becomes very difficult for the antivirus software to determine whether the system or a particular file is corrupt. There are many viruses which remain in disguise and it becomes difficult for the antivirus system to detect their presence. This is why it is necessary to choose from the Top Three best computer Antivirus Software only. Buying an efficient computer viruses protection software is very necessary to combat them. Hackers and unscrupulous people are busy creating newer viruses and other programs regularly and hence a constant update of virus database is a must for the antivirus software.