Types of computer virus

There are all types of computer viruses but what is a computer virus? A computer virus has been defined as a set of computer instructions that reproduces itself and it may attach to other executable code. Usually this code is a short program that may either embed in other code or stand on it's own. In essence, this computer program is designed to infect some aspect of the host computer and then copy itself as much and as often as it has the chance.

It was estimated that a virus by the name of mydoom infected well over a quarter a million computers in one day back in 2004. There are tens of thousands of worms and viruses now being spread via the internet with new ones being discovered each and every day. It is often through quite innocuous and normal internet activities like the exchange of files like music, photos and others that many people are infected with these unwanted and sometimes dangerous programs.

The nomenclature that is now used to describe viruses has changed considerably over the last few years as more, if not most, computers are now on the internet. This has ushered in a change in the types of computer viruses toward a worm/virus hybrid and has caused the distinction between them to vanish.

There are a whole group of people that spend a tremendous amount of time looking for what have been termed backdoors into your computer so they can find ways to inject their code into your computer and use it for their own intentions.
How Does A Virus Spread

One of the intents of all types of computer viruses that gets installed on your computer will be to spread itself. This happens in a fashion that is not all that different from what happens with a virus in the human population. It is through exposure that the virus spreads when the computers defenses are down or non existent. Also like their biological counterpart the computer virus can be spread rapidly and are not very easy to get rid of.

Because the way a virus operates is to be stealthy, coupled with the rapid communications that happen between today’s computers, it is easy to dramatically increase the speed at which a virus that is targeting a newly discovered vulnerability can move around the web and around the world.

A virus that targets a network of computers can even more easily spread since so many computers are connected and most likely will have the same vulnerability and easy access to one another. Often viruses will spread via shared folders, email or over other media that is often exposed to other computers via removable media like cds and flash drives.

Because there are so many types of computer viruses, a virus can infect another computer unintentionally anytime that program is run and the virus is activated. Something like opening a email attachment or downloading a file off the internet or giving or receiving a copy of a program or file from a co-workers thumb drive can expose you and others to a computer virus.

Literally the gamut of these types of computer viruses can expose you whenever you have a downloaded file or a external drive attached to your pc. The most common way they spread is via email attachments or with the use or transfer of files via instant messaging.

The Types Of Computer Viruses

There are six broad categories or types of computer viruses:
1. Boot Sector Virus
2. File Infection Virus
3. Multipartite Virus
4. Network Virus
5. E-mail Virus
6. Macro Virus

Boot Sector Viruses

Viruses that aim at the boot sector of a hard drive are infecting a very crucial component of the boot process. The boot sector holds critical information that controls the hard drive and also the part of the operating program that is in charge of the whole boot process. These types of computer viruses go a long way toward the assurance they will be successful in their mission by absolutely loading into the system memory while the boot cycle is starting.

Unlike other viruses the boot virus does not affect files, instead it goes after the drive itself on which the virus is saved and this is part of the reason that it is no longer as big a threat as it used to be. Since the advent of cds and dvds and the drives that carry them it is not possible to infect the programs that they carry. In the days of floppy drives the virus could spread quite quickly from computer to computer via the disks but since it is not possible to infect a cd or dvd this virus has become almost a non threat. Another reason this types of computer viruses have become less common is that now operating systems stand guard over the boot sector and that makes it very hard for the virus to have any effect.

File Virus

File viruses are coded so that they will attach themselves to exe files, compressed files like zip files and driver files. The can be set into actions when the program they are attached to is started. Then after the virus is set into motion it will attach itself to other programs and system files and start along it's intended path for which it was written. So you see it is a two prong approach. First depending on the types of computer viruses it will duplicate and then go about its intended mission. The virus will search through the programs in the system and find places to infect with the code and then it will activate when that program is run next time. It will continue to duplicate until it is all over the computer and probably any computer that is attached to the original system.

Often these viruses will harbor special code that causes them to be activated when certain events take place. The event often is a date or some other trigger event that is easily defined on any computer system you may have.

Multipartite Viruses

That which has been termed the multipartite virus are the types of computer viruses that are both a file virus and a boot sector virus. They enter the computer via various sorts of media and then embed themselves in the system memory. They then go into the hard drive and infect the boot sector. Once installed in the boot sector these types of computer viruses infect executable files and spread themselves in the system.

This is another virus that has past its prime for various reasons but in times past these types of computer viruses were responsible for many infections because they combined characteristics of two different viruses into one.

Network Viruses

A virus that is especially made for networks is uniquely created to quickly spread throughout the local area network and generally across the internet as well. Most of the time is moves within shared resources like drives and folders. Once it finds entry into a system it will search for vulnerable computers in the network and likewise infect that system and do the same again and again always on the hunt for new vulnerable systems.

E-Mail Viruses

Most of the time a e-mail virus is one of those types of computer viruses that is generally a macro virus and it will multiply itself by seeking out the other contacts in a e-mail address book and then send itself to those addresses in hopes that they will activate the virus too. Thus it spreads over and over again exponentially. There are even times an email virus can spread by only previewing it in the mail client. One that was very successful in spreading worldwide was the ILOVEYOU virus and it was destructive too.

Macro Viruses

Macro viruses as the name implies, will infect files of programs that use macros in the program itself. The most common of these are the Microsoft Office files created in Excel spreadsheets, Word documents, Access databases, Powerpoint presentations and these type of files from AmiPro and Corel Draw and others.

One should always be on the lookout for these types of computer viruses and should take every precaution to avoid them. Be ever watchful of every file you open or else you may be looking for my next hub on how to remove these types of computer viruses.