What are the Different Types of Viruses?
• File viruses. These viruses are essentially programs themselves. They infect other executable files (usually with the file extensions .COM or .EXE), and when you execute one of these files, you activate the virus as well. These viruses spread when you share infected program files, either by diskette or through network transfer. • Boot sector viruses. These viruses are common, but you can avoid them relatively easily. A boot sector virus moves to a new system when an infected diskette, accidentally left in the diskette drive when the computer’s shut down, is still in place when you turn on the computer. The computer tries to boot (or start up) from the diskette, and the virus moves from the diskette to your system. Anyone who has booted a computer with a diskette in the drive and received a “Non-system disk or disk error” message has made their system vulnerable to this type of virus. That’s all it takes, and even factory-sealed software can contain boot sector viruses. • Multipartite
Viruses are tiny bits of genetic material, wrapped in protein envelopes, capable of hijacking the cellular machinery of plants, animals, and bacteria for self-replication. Viruses are extremely small, much smaller than bacteria. A typical virus is between 10 and 300 nanometers (billionths of a meter) in size, whereas typical bacteria are larger than a micrometer (millionth of a meter) in size. Only about 30,000 virus types are being tracked by virologists, although millions likely exist. Viral classification is made difficult by a lack of fossil evidence — viruses fossilize poorly — and controversy over whether viruses are living organisms or not. Unlike other organisms, new viruses sometimes emerge de novo from the genomes of preexisting organisms, making it difficult to build coherent family trees. However, this doesn’t stop virologists from trying. A unified taxonomy for viruses was only developed in 1966, by the International Committee on Taxonomy of Viruses (ICTV). This classifica
