A virus is an unwanted application (software program) that attaches itself to your computer without your knowledge. It attempts to reproduce itself and change or delete files under specific circumstances. For example the virus might be activated each time a specific day of the month, or when a specific file is opened, or when certain actions are observed. This activation is referred to as the “payload”. Some viruses do nothing but reproduce themselves. Some perform trivial extras like beeping the keyboard, or forcing the file to be saved in a specific format. Some are more destructive and attempt to rename or erase files or destroy the hard drive. There are many varieties of viruses, each with a specific set of actions it intends to complete.

Macro viruses are programming code, created by hackers or unethical programmers, which is either annoying, prankish or harmful. The macros are written to attach themselves to the default document of a software package such as Word or Excel. When an unsuspecting user opens a document containing a macro virus, the virus attaches itself to the default document. Each time a document is created or edited from this time forward, the virus attaches itself to that document. The problem escalates as the document is passed on to other computers by file sharing or e-mail. The virus continues to spread until it is removed.  Boot sector viruses attach themselves to the part of the disk that is read by the computer when it starts up. The boot sector contains important information about the disk. In most cases, the virus relocates this information to another location and displays its own code.

A computer virus is a program and not a microorganism, but it is infectious and can be highly complex. Viruses implant instructions in other programs or storage devices that can attack, scramble, or erase computer data. They are often obtained by downloading executable software from emails, the web or social networking sites.  It is usually the unwary who get computer viruses. ALWAYS run virus detection software on your computer.  Equally important, however, is updating the program regularly.  This is similar to getting a flu shot each year because the strain of flu changes somewhat from year to year.  You must get the latest update to be sure that your computer is protected from the latest strain of computer viruses.  ALWAYS keep a back up of important files in case your computer does get a virus (or has another form of failure).  Obtain new software from reputable sources and check new software (and other files) with virus protection software before saving to your hard drive.

A Trojan Horse is similar to a virus, in that it is a malicious, security-breaking program that is disguised as something benign, such as a directory lister, archiver, game, or (in one notorious 1990 case on the Mac) a program to find and destroy viruses! When these programs are executed, the embedded virus is executed too, thus propagating the `infection’. This normally happens invisibly to the user.  It cannot, however, infect other computers without assistance, such as downloading files from websites. The virus may do nothing but propagate itself and then allow the program to run normally.

Virus problems are terribly costly to individuals and to businesses.  The best defense is virus protection software and frequent updating of the protection files.