· File viruses: These viruses attach themselves mostly to executable viruses. Some will replace the normal program’s instructions with its own. This means that when the user opens the file, he/she will see the virus’ display. Other viruses will change the original extension of the file from .COM to .EXE, thereby making the computer load the virus before the actual program.· Boot viruses: The boot viruses hook into the boot sectors of a floppy diskette or into the MBR (Master Boot Record) of the hard drive. When the user boots the computer, the virus infects the computer and the code enters the memory. The virus will remain in memory and will infect any floppies that are used. Much as a time bomb is set for explosion at a defined time, usually boot viruses are launched on a specific date or at a specific hour. · Multi-partite viruses: A virus of this sort is a cross of a file virus and a boot virus. They combine the worst of both types of viruses.· Macro Viruses: These viruses are the new rising star of viruses. They infect ordinary software files and are not that complicated to write. This means that their numbers will continue to rise as more powerful programs use macros. Although most have no real damaging payload, they are annoying as they can affect the performance of the program. They can be found mainly in Word, but have also targeted Excel and Ami Pro. Do viruses have different features to them?
Viruses do have different features to them. The following features can be found in any of the aforementioned categories.· Stealth viruses: A stealth virus will hide from any program that will look for it. It achieves this by hooking interrupts, thereby making everything look normal to the user. Stealth viruses can report false dates and file sizes to the user. · Polymorphic viruses: Each time these viruses infect they change their form. They use encryption to conceal themselves from the anti-virus program. This makes it harder to detect the virus. How do they spread?
Viruses can be in a wrapped software product that is loaded onto the computer from a floppy diskette. They can come from purchased hardware. Viruses can be in a downloaded file from the Internet or in an attachment to an e-mail. The most probable way of receiving a virus is on a borrowed diskette from a friend or colleague. How do I know that my system is infected?
Much like their physical counterparts, many computer viruses will cause symptoms to appear in the host.