A computer virus is a computer program that can copy itself and infect a computer. The term “virus” is also commonly but erroneously used to refer to other types of malware, including but not limited to adware and spyware programs that do not have the reproductive ability. A true virus can spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive.
Viruses can increase their chances of spreading to other computers by infecting files on a network file system or a file system that is accessed by another computer.
As stated above, the term “computer virus” is sometimes used as a catch-all phrase to include all types of malware, even those that do not have the reproductive ability. Malware includes computer viruses, computer worms, Trojan horses, most rootkits, spyware, dishonest adware and other malicious and unwanted software, including true viruses. Viruses are sometimes confused with worms and Trojan horses, which are technically different. A worm can exploit security vulnerabilities to spread itself automatically to other computers through networks, while a Trojan horse is a program that appears harmless but hides malicious functions. Worms and Trojan horses, like viruses, may harm a computer system’s data or performance. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious or simply do nothing to call attention to themselves. Some viruses do nothing beyond reproducing themselves.
Fame, Fear, and Loathing
Fame does not always equate to power, financial punch, or pervasiveness in the virus world. Media attention, AV software vendor marketing, and other factors influence what makes a virus famous, even if it’s not that damaging.
I have heard of some of these viruses, and despite my wide number of clients, friends, and exposure of my own computers over the years, I never saw or caught some of them.
As the Internet has become more and more a part of everyday life, and computing spreads to every phone, DVR, and other electronic device, the future holds potential for even more widespread and famous viruses than any of these. Let’s look at the top ten for clues to what the future may hold.
The Top Ten
1. ILOVEYOU – (2000) One of the most widespread and rapidly spreading viruses ever, the ILOVEYOU virus spread via e-mail, posing as an executable attachment sent by a friend from the target’s contact list.
2. Code Red – (2001) IIS on Windows servers were the target of this virus. It also launched denial of service (DoS) attacks.
3. Nimda – (2001) Nimda used seemingly every possible method to spread, and was very effective at doing so. Nimda is notable for being one of the fastest spreading and most widespread viruses ever.
4. Melissa – (1999) The Melissa virus is notable because it is a Word macro virus. It cleverly spread via e-mails sent to contacts from the infected users’ address books.
5. Sasser – (2004) Sasser exploited a buffer overflow and spread by connecting to port 445 on networked Windows systems. The chaos caused was possibly the worst ever, as systems restarted or crashed.
6. The Morris Internet Worm – (1988) The grandfather of computer worms, the Morris worm infected Unix systems and was notable for its “accidental” virulence.
7. Blaster – (2003) Blaster exploited a Windows operating system vulnerability and let users know of its presence with a system shutdown warning.
8. SQL Slammer – (2003) This tiny virus infected servers running Microsoft’s SQL Server Desktop Engine, and was very fast to spread.
9. Elk Cloner – (1982) Despite Apple’s marketing that their systems are less prone to viruses that was not always the case. Notable as possible the first personal computer virus, Elk Cloner infected the boot sector of Apple II floppies.
10. Creeper – (1971) This is noted as possibly the first ever computer virus. It infected computers on ARPANET. Mostly harmless, the concept of Creeper has infected the minds of rogue programmers through today.
Of phones, portable music players, game consoles, DVRs, car computers and GPS devices, only phones so far have been a significant target of virus writers. None of these systems has a well-developed anti-virus platform and network yet all of them can connect to the Internet and are potentially vulnerable. The ubiquity of Windows systems makes Windows CE devices a prime and continuing target.