Computer VIRUS i.e Vital Information Resource Under Seize are considered as very first form of computer threats. Computer VIRUS usually replicate themselves, damage your files and are also able to distribute themselves on network. Virus is usually a executable file. It may be different or same for different Operating system.
Most of the times virus disguise themselves as system files so that they can avoid detection. Their detection prevention mechanism is so strong that a common user can never figure out, whether a file is virus or just another system file or data file.
Viruses can be classified as follows:
Boot Sector Virus:- Boot sector viruses or MBR Viruses are responsible for damaging boot records of a system. When executed they copy themselves in boot sector and load themselves every time the system starts.(MBR i.e Master Boot Record is the record stored on hard disk or bootable CD which stores information about startup of system. In other words files stored in MBR are the very first thing that is loaded in memory for execution.). Examples of boot sector virus are Form, Michelangelo, Stone, Disk Killer etc.
File Virus:- File virus, as its name suggests are made to damage your files. They can also damage your program files and hence also known as Program Virus. They usually infect executable files, system files and driver files. Example of file virus are Sunday, Cascade etc.
Multipartite Virus:- Multipartite virus are hybrid viruses. They have properties of both boot sector and file virus. So they are more dangerous than first two mentioned above because they not only infect boot sector but also system files. Common examples are Invader, Flip and Tequila.
Stealth Viruses:-Stealth viruses are able to hide themselves to avoid detection They can store themselves in memory during scanning by Anti-Virus Programs and get restored when scanning is over. Due to their this type of stealthy nature they are named as Stealth Virus. They are so well programmed that they can even hide themselves inside other files without increasing size of file. This is also one of the mechanism they use to survive from Anti-Virus Programs. These viruses are one of the most difficult viruses to detect. Common examples are Frodo, Joshi, Whale etc.
Polymorphic Viruses:- A virus that can encrypt its code in different ways so that it appears differently in each infection. These viruses are more difficult to detect. Common examples are Involuntary, Simulate, Cascade, Pheonix etc.
Macro Viruses: Virus that infects the macros within a document or template. When you open a word processing or spreadsheet document, the macro virus is activated and it infects the Normal template (Normal.dot)-a general purpose file that stores default document formatting settings. Every document you open refers to the Normal template, and hence gets infected with the macro virus. Since this virus attaches itself to documents, the infection can spread if such documents are opened on other computers. The very dangerous thing about these viruses is they are not platform specific that means a code once written can infect any OS. Common examples are DMV, Word Concept etc.
Active-X Virus: Active-X viruses are under emerging stage. They are usually executed on victims PC via web browser. The JAVA scripts, Perl scripts, Flash scripts enabled on victim’s PC without any Firewall, Anti-Virus, Internet Security Suite can easily obtain access to PC. Keeping Video and Audio plug ins ready without protection can bring Active-X Virus to your party.
How you can keep your computer virus free:
Following are some simple tips that will help you keep your computer safe from viruses,
1.Never open any pen-drive by double clicking on it open it by address pane from my computer.
2.Always keep your auto play option off.
This is how you can do it, for windows xp from start menu, click on run command write “gpeit.msc” and press enter “group policy editor” will open in front of you, now navigate user configuration–>administrative templates–>system, find out “turn off autoplay” and make it enabled. For vista and 7 you can directly turn it off by control panel.
3.If you are buying a computer make sure you buy only original OS for it, a legal system gets updated and also gets support from vendors. A pirated copy of OS may itself contain any malicious code that may even help viruses to stay hidden from anti-virus.
4.Always keep your system and anti-virus updated and use firewall while on Internet.
5.Always keep hidden folders option and hide file types disabled, to do this open any instance of “explorer.exe” goto tools–>folder options–>view
now disable options “do not show hidden files and folders” and “hide extensions of known files“. This will help you keep eye on suspicious files and folders.