7 Major Types Of Computer Viruses

1. Boot Virus
A virus written into the boot sectors of a floppy disk. A popular way to spread a virus when floppy disks were widely used, the boot virus relied on people forgetting to remove the last floppy they inserted when they turned the machine off. When turned back on, the machine read the boot sector program, which normally loads the operating system, but ran the infected program instead. Once infected, the boot virus replicated itself onto all subsequent floppies used in the machine. The Michelangelo virus was a famous boot virus that infected the computer on March 6th, Michelangelo's birthday.

2. File Infector
A role of a file infector is to directly strike and modify an application, usually seeking out EXE. or COM extensions. When the application is started, the infection is executed and does whatever it has been commanded to do. It is typically installed into system memory. There it waits for something to trigger it and corrupt other items. This infection is most commonly distributed via compromised networks, over the web or from a corrupted floppy disk. One of the most malicious forms of the file infector goes by the alias Win32. Its purpose is to transfer hits to the HttpSendRequest into a corrupted .DLL format. This type of file infector is often installed by other malware. This infection will corrupt other items and usually result in the crash of a web browser. This file infector employs a technique to make sure its corrupted .DLL format will replace the target extension found within the system. When the computer is restarted, it unknowingly boots the infected content.

3. Macro Virus
A type of computer virus that is encoded as a macro embedded in a document. Many applications, such as Microsoft Word and Excel, support powerful macro languages. These applications allow you to embed a macro in a document, and have the macro execute each time the document is opened.
According to some estimates, 75% of all viruses today are macro viruses. Once a macro virus gets onto your machine, it can embed itself in all future documents you create with the application. Antivirus programs can protect your system against most macro viruses, although new ones are always being created that slip by the antivirus filters.

4. E-mail Worm Virus
A virus that comes within an attached file in an e-mail message. When that file is opened, the virus does its damage. Macro viruses can come in Microsoft Word documents that are sent as e-mail attachments. The macro causes the damage when the document is opened providing macro processing has not been disabled within the Microsoft Word application.

5. A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack)
is an attempt to make a computer resource unavailable to its intended users. Although the means to carry out, motives for, and targets of a DoS attack may vary, it generally consists of the concerted efforts of a person or people to prevent an Internet site or service from functioning efficiently or at all, temporarily or indefinitely. Perpetrators of DoS attacks typically target sites or services hosted on high-profile web servers such as banks, credit card payment gateways, and even root nameservers.

6. Hoax Virus
A virus hoax is a false warning about a computer virus. Typically, the warning arrives in an e-mail note or is distributed through a note in a company's internal network. These notes are usually forwarded using distribution lists and they will typically suggest that the recipient forward the note to other distribution lists.
If you get a message about a new virus, you can check it out by going to one of the leading Web sites that keep up with viruses and virus hoaxes. If someone sends you a note about a virus that you learn is a virus hoax, reply to the sender that the virus warning is a hoax.

7. Multipartite Virus - hacker

Uses more than one Means of Transmission or more than one Means of Infection. An example is the infection of an executable program and the boot sector, such that a mutual re-infection can take place after one of the two infections is detected and removed, thus keeping the virus alive.