There are a fair amount of different types of viruses. I will go over what they are, how they are spread and what they do. I might even include a few examples of the more popular viruses if I get around to it.
File Infector Viruses
The most "Traditional" form of a computer virus is a file infector virus. It injects itself and hides within the code of another program. The program it injects itself into can be anything - as long as it's executable (Some common file extension examples are: EXE, COM, SYS, BAT and PIF). When the infected program is launched, the virus code copies itself to your computer's memory, typically before the original program code is launched. By loading itself onto your system's memory, the virus can continue to run even after the host program is shut down. Before the internet, file infector viruses accounted for an estimated 85% of all virus infections. That number is, however, down, because of the many ways to spread viruses through the internet now-a-days.
Boot Sector Viruses
Boot sector viruses live in the part of the disk that is read into memory and executed when your computer boots up. Once loaded, the virus has potential to infect any other disk, be it a CD, floppy disk, SD card or anything of the sort. A disk-based boot sector virus can also infect a PC's hard disk. Most boot sector viruses were spread through the use of floppy disks, mostly in the days when hard disk's were less common. Since removable disks are far less used today, especially to boot up, the risk of being infected by a boot sector virus is low.
Macro Viruses
Some viruses are created with the macro capabilities of some software. Macros are small programs designed to do very specific tasks within an application. The most common macro language, used in all Microsoft applications is VBA (Visual Basic for Applications). VBA code can be added to a word document to create customs menus and perform automatic operations; unfortunatley VBA code can also be used to modify files and send unwanted e-mail messages automatically. What makes macro viruses particularily dangerous is that macros - and thus macro viruses - can be attached to word documents. Most virus types, especially the older ones, had to be imbedded in executable files, which made them relatively easy to find, delete and stop. But when a document file can be infected, and most users open documents without any second thoughts, its far easier to become infected. Hence, most users who are usually super-vigilant about downloading files often open documents, like said above, with no second thoughts. Because data and word files are shared so freely, especially in corporate networks, it is very easy for macro viruses to spread.
Script Viruses
Script viruses are based on common scripting languages typically used on webpages and in some programs. These viruses are written in JavaScript, ActiveX and Java applets, which commonly run automatically when you visit the webpage. With the increasing use of people browsing the web, these script viruses are becoming far more common, and more deadly. The good news is, however, that if you have real-time web scanning enabled, and the warning bar shows up, you have a fairly low chance of being infected.
Trojan Horses
A trojan horse is a program that claims to do one thing but does something totally different. A typical trojan horse has a filename that makes you think it's innocent enough, and safe to open. But when you open this file, its actually a virus program that proceeds to inflict damage to your system. It delivers it's payload through deception, and the name is based on the Trojan Horse in the work of fiction. Trojan horses are becoming more common, mostly through email. Some trojan horses might even claim to be anti-virus applications but turn out to be deadly, system-wrecking applications.
Worms
A worm is a particularily nasty type of virus that scans the internet or a computer or possibly even a specified network that has a specific security hole. It then copies itself to the new machine through the security hole and then starts replicating itself there and scanning for new targets off the new system. Worms replicate VERY quickly, a network with one computer infected with a worm can be brought to it's knees in a matter of hours. Worms don't nessicarily have to be delivered through conventional file-sharing activities; so called "file-less worms" are recent additions to the virus lists. While operating, these worms exist only in system memory, making it VERY difficult to catch, identify and remove them. These worms could cause large amounts of damage in the near future.
Thu Aug 31, 2023 9:03 pm by chriz101
Subject: Understanding Viruses and Types of Viruses For Beginners 
