Computer Viruses

The most common form of cyber attacks are computer viruses. A computer virus is a program created specifically to invade a computer and/or computer network with the purpose of disrupting productivity, stealing information and/or destroying data. A virus is a program or set of instructions that will execute normally without the users consent. “According to a survey conducted by America Online (AOL) 20% of home computers connected to AOL were infected by a virus or worm, and 80% of the computers were infected by snooping programs such as Spyware\Adware”. (Roberts, Your PC May Be Less Secure Than You Think, 2004) According to Computer World Magazine; “it is also estimated that PC Viruses cost businesses approximately fifty five Billion in damages during the year 2003, in 2002 the cost was between twenty and thirty billion and at thirteen billion in 2001. (Roberts, Your PC May Be Less Secure Than You Think, 2004) A computer virus is a malicious program that can destroy files, disrupt your networks or use your computer system to attack others. Computer viruses are most commonly categorized in different ways, however the two most used ways to classify a computer virus are by the way they spread and by what they do. (Microsoft, 2009)

Classified by how they spread there are four major groups of computer viruses.

• Trojans: enters a system disguised as something else and sends its creator/owner the system information and then it waits for the creator/owner to access the infected system. Once the programmer has access to the system all of the data is vulnerable to theft and all of the contacts found become potential targets.
• Worms: a virus which spreads on its own by hijacking email accounts, file transfer programs, and other file transmitting applications. The worm will either sit dormant until the programmer accesses the system or it may perform certain tasks which are usually information theft.
• Bomb: another type of virus, however it doesn't propagate, it is sent to a target computer by human intervention and once there it waits to be activated by a trigger such as time or event. Once it goes off it usually does unpleasant things to the target computer or others.
• Port Scanners: hides in a system and scans for IP addresses and open ports with in the surrounding network, once it has collected some data it then makes available to other malicious code or the originator of the code. (Secureurpc, 2009)

Classified by what they do there are seven major groups of viruses.

• Boot Virus: Infects the boot sector of disk drive rendering it unusable. That means that the infected computer will no longer boot an operating system.
• Program virus: Infects executable programs such as word, excel and others in order for it to run. It then performs the task it was designed to do.
• Multipartite Virus: The combined Boot and Program Virus.
• Stealth Virus: Avoids detection by removing itself from the system registry, doubling for a system file, hiding under program groups, etc.
• Parasitic Virus: Embeds itself into another file or program.
• Polymorphic Virus: Changes its code structure and generates executables at random in order to avoid detection.
• Macro Virus: Exploits the macro language of programs such as Microsoft Word, Excel and others for malicious purposes. (Webopedia, 2007)

According to Message Labs who provides an antivirus service for inbound/outbound email inspection for more than 8,500 businesses worldwide “during the MyDoom outbreak; They Processed between 50,000 – 60,000 new copies of the virus per hour, collected over 1.2 Million copies of the virus and at peak infection, about 1 in 12 emails contained MyDoom.” (Roberts, 2004)