Computer Viruses are little bits of software that normally have a negative impact on our computers when they are activated. Usually viruses are attached onto other software programs (games, disk utilities, office documents/Macros, screen-savers), and are activated when these normally harmless programs are started. A virus is inactive until the infected program is run or an infected boot record on a DVD, USB flash drive or CD is read. When the virus is activated it loads into your computer's memory where it can perform its nasty job or spread itself to other programs on your system or computers in your network.
USB storage device used in an infected system (or CD-Roms/DVDs burned on an infected system) can then carry the virus to another machine. Programs downloaded from Internet, or file-sharing programs can also spread a virus. Email is the number 1 way to spread viruses, Trojan horses and especially internet worms.
It should be made clear, that Internet and file-sharing programs do not create viruses or infected files in any way. It is certain anti-social people who create viruses, and then use these services to spread the infected files to other users on the system.
This is very similar to cars and highways in that Ford, Toyota or the highway makers do not cause traffic accidents, it is the people who got drunk and then drove who causes a 14 car pileup. Of course if there weren’t cars or highways there wouldn’t be an accident… then again, the person would still be getting smashed and driving his horse-carriage into the store window.
For a virus or similar program to have any great impact it needs to be able to spread from one machine to another. They are specifically designed to get access to parts of your computer system that allow for communication with other machines. Below is a discussion of some of the most common methods.
Every disk (hard disk, CD, DVD) contains a section called a boot sector whether it is a bootable disk or not. When a computer is turned on, it looks for boot information (start-up instructions). If the it finds a disk with boot information, it reads that information and uses it to properly start the computer. If for some reason that boot information is infected with a virus, the virus is activated and possibly transferred to the computer's hard drive (if the infection was on a CD for example).
Once the boot code on the hard drive is infected the virus will be loaded into your computer’s memory every time you start your computer. From memory the boot virus can travel to any and every disk that is put into your computer. This is how the infection spreads.
Most boot viruses could be on a system for a long time without causing problems, simply existing there to spread themselves. Often such viruses are designed to activate their bad behaviour on a specific date (Halloween for example). There are some nasty boot viruses that will destroy the boot information or force a complete format of the hard drive immediately after they get into a computer.
When an infected application is run on your Computer the virus activates and is loaded into memory. While the virus is in memory any new program file that you run can become infected. This means that there will be increasingly more applications on your system that are infected. Multiple infections are very common and will certainly cause system problems.
Program files may function without any problems for some time but eventually they will have problems or multiple infections brings the entire computer system down. The data the program produces may be a first sign of infection such as saving files without proper names, or with incorrect/incomplete data being saved.
Viruses of this type are often designed to seek out programs that are used to share information between users/computers such as email applications, screen savers, office document Macros, and self-extracting compressed files.
Many of the most dangerous viruses are primarily spread through e-mail attachments - files that can be sent along with an e-mail message. In such cases, the user of an infected computer unknowingly attaches an infected file to an email message, and then sends the email to a friend or colleague. When the email is received, the virus is launched when the file attachment is opened, thus infecting a new computer. Email messages with animations, automated greeting cards, jokes, photographs, spreadsheet and document files, all have been documented to contain virus files.
More and more frequently these days mass mailing email worms/viruses are being released. These attacks AUTOMATICALLY scan your computer’s files and address book for any email address it can find and then uses your email application to AUTOMATICALLY send infected messages to any email address found in any file on your computer (not just email message files).
USB flash drives are a very common way viruses being spread from machine to machine. Anyone with an infected machine, using a flash drive to copy and save files, can also copy and transfer the virus. Any use of that same removable storage device , by any user, at any time in the future, will most likely contaminate, or re-contaminate the any computer it is used with.
With CD’s, all the above holds true with the exception that an infected CD can never be cleaned. To get rid of an infected CD, you need to put it in the trash and never use it again.
Peer-to-Peer network, Local Area Networks (LAN), a Wide Area Network (WAN), Wireless Networks, and the Internet, are all computer networks. They all have the same basic purpose; to share software, and information resources between two or more computers. As with anything else that is shared between computers, networks let users share files, and wherever files are shared, viruses can be shared and spread.
Most network virus/worm/Trojan activity is like what we described earlier, although more and more examples of automatic mass mailing attacks, system resource attacks are being found. Recently many attacks are designed to specifically target major corporate interests (Microsoft, eBay, FaceBook, Amazon, major Banks etc.) in an attempt to disrupt their online services. Very generally these are called DOS (denial of service) attacks. The way they most commonly work is by secretly infecting thousands of local user computers (like the one you are using right now), and then at a specific time, launching a combined attack from all the infected machines against the primary target.
As you can see, your computer can be hijacked without your knowledge and then used in a major attack against an unsuspecting company. However with up-to-date virus/firewall protection, your computer will be immune to such hijacking.
Other sources of viruses have been found to be the result of software downloads available over the Internet. Software patches, drivers, demonstration software, from reputable companies, generally carries little risk. However, the Internet is also filled with "unofficial" software, pirated programs, and low-budget software from questionable sources that may be intentionally or unintentionally infected with viruses. Files downloaded directly from the Internet (either through file-sharing programs or direct download from websites), are among the fastest growing sources of computer virus infections.
Email, with its nearly universal availability and ease of use; chat rooms and messenger systems, not only make communication simple and quick, also make the transmission and re-transmission of infection simple and alarmingly fast. Creators of newer viruses, and internet worms specifically target these systems because they are widely used, and are often built right into the operating system and used with default settings making them much easier to attack and exploit.
As a point of reference, Internet Explorer, and Outlook/Outlook express email clients are two of the applications most targeted by internet viruses and worms. Why? Because they are installed on more computers around the world than any other software, and they are installed 99% of the time with default settings (which means virus programmers have an easy blueprint to follow).
If you use an email system or instant message system that is installed automatically with your computer’s operating system you need to install and use current antivirus software. You also need to learn how to turn off certain default settings that can leave your system open to very easy attack. Visit How to keep your computer from spreading viruses page to learn simple steps to stop spreading Computer viruses.
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