Computer Viruses

There are many types of invaders in the computer world including virus's, worms and trojan horses. They come in many types and come into your computer in many ways. There are ways to protect your computer from these nasty things however, you must keep on protecting it and not let your guard down.

According to wikipedia.com a virus is a "self replicating computer program that spreads by inserting copies of itself into other executable code or documents". Just as a biological virus spreads itself from cell to cell and host to host in humans a computer virus spreads from file to file and computer to computer. It has been argued whether the first viruses were malicious or just programming experiments that went out of control. Originally computer viruses were spread by primitive networks and by disks that became infected and were passed from one person to another. Many computers were originally infected by dreaded boot sector viruses but as technology has changed so has the way that viruses are delivered and boot sector viruses have all but vanished. A large majority of today's viruses are spread by e-mail attachments. Also most viruses now are infected executable files or are hidden in compressed zip folders. There are many types of macro virus scripts that will infect programs such as word processing and accounting programs by manipulating these scripts to transfer from one infected file to another. Viruses can infect a file in many different ways. Parasitic viruses modify the code of the infected file leaving it partially or fully intact and inserting the code somewhere at the beginning, the end, or in an empty area somewhere in the middle. Overwriting viruses just simply place there code over the code of the original program rendering it useless. Companion file viruses do not modify the original file but instead create a duplicate file containing the virus. Then when a user tries launching an the file the infected version launches first.

A leading antivirus software company Kaspersky Labs says on there virus information website Viruslist.com that today the most common and dangerous computer threat is Trojan programs. There are eleven types of programs classified as Trojans; Backdoor Trojans, General Trojans, PSW Trojans, Trojan Clickers, Trojan Downloaders, Trojan Droppers, Trojan Proxies, Trojan Spies, Trojan Notifiers, ArcBombs, Rootkits. Of all these Trojan programs, Backdoor Trojans are classified as the most dangerous type and the most widespread. Backdoor Trojans work in the same way that remote administration software works, allowing someone to completely take over and control a machine over the internet or LAN. The only difference between remote administrator software and a Trojan sometimes is that the Trojan is installed without the knowledge or permission of the machines user. General Trojans damage a victim's machine and threaten data integrity. PSW Trojans steal passwords and user names from a victim's machine. They sometimes steal system passwords, e-mail information and passwords, system details (such as OS type, disk space and memory available), registration details, IP addresses, and sometimes even passwords for online games. Trojan clickers, also know as redirect Trojans, attack a victims machine and redirect internet browsers to specific websites with the intent of increasing hit-count for advertising purposes, or to perform DoS (Denial of Service) attacks on specific sites and servers, or to lead the machine to another infected resource such as a virus. Trojan Downloaders work with the purpose of intentionally downloading and installing malware and adware onto the attacked computer. Trojan Droppers work in many ways like a Trojan Downloader, but they instead include the other malware within themselves. Trojan Proxies function as a proxy server and provide anonymous access to the internet, but also can use connected machines for massive mailings of spam. Trojan Spies consist of a variety of spying programs that can log keystrokes, screenshots and log activity of applications. These Trojans are also very dangerous as they are used to steal banking and other financial information to support online fraud and identity theft. Trojan Notifiers are usually