A virus is a program designed to infect and potentially damage files on a computer that receives it. The code for a virus is hidden within an existing program—such as a word processing or spreadsheet program—and when that program is launched, the virus inserts copies of itself into other programs on the system to infect them as well. Because of this ability to reproduce itself, a virus can quickly spread to other programs, including the computer's operating system. A virus may be resident on a system for a period of time before taking any action detectable to the user. The impact of other viruses may be felt immediately. Some viruses causes little or no damage. For example, a virus may manifest itself as nothing more than a message that appears on the screen at certain intervals. Other viruses are much more destructive and can result in lost or corrupted files and data. At their worst, viruses may render a computer unusable, necessitating the reinstallation of the operating system and applications.
Viruses are written to target program files and macros, or a computer's boot sector, which is the portion of the hard drive that executes the steps necessary to start the hardware and software. Program viruses attach themselves to the executable files associated with software programs, and can then attack any file that is used to launch an application, usually files ending with the "exe" or "com" extensions. Macro viruses infect program templates that are used to create documents or spreadsheets. Once infected, every document or spreadsheet opened with the infected program becomes corrupted. Boot sector viruses attack the computer's hard drive and launch themselves each time the user boots, or starts, the computer. Viruses are often classified as Trojan Horses or Worms. A Trojan Horse virus is one that appears harmless on the surface but, in reality, destroys files or programs. A Worm attacks the computer's operating system and replicates itself again and again, until the system eventually crashes.
VIRUSES AND THE INTERNET
The Internet, with its global reach and rapid delivery times, provides the ideal breeding ground for viruses. Typically, someone who wants to spread a virus does so by sending out an email message containing an infected attachment. The subject line on such a message sounds innocuous, so unsuspecting recipients open the message, unwittingly infecting their computers.
An email message was used to spread the so-called Love Bug virus in 2000. The most destructive virus to date, it targeted users of Microsoft's Outlook email program. Originating in the Philippines, the Love Bug message's subject line was the inviting "ILOVEYOU." If a user opened the message's attachment, the virus quickly began to destroy files, targeting digital pictures and music files. The Love Bug virus also perpetuated itself by forwarding the original message to all email addresses listed in the current recipient's Outlook address book. In this way, the virus was able to circle the globe in just two hours. The virus brought businesses to a standstill as companies, large and small, were forced to shut off incoming Internet email messages and repair infected systems. In all, the Love Bug virus is estimated to have cost up to $10 billion in lost work hours.
With an estimated 40,000 viruses already identified and some 300 new viruses created each month, keeping a computer free of viruses is a daunting but not impossible task. The following are steps every computer user should follow to protect his or her computer from viruses.
1. Install an anti-virus software program to identify and remove viruses before they can cause any damage. These programs scan, or review, files that may come from floppy diskettes, the Internet, email attachments, or networks, looking for patterns of code that match patterns in the anti-virus software vendor's database of known viruses. Once detected, the software isolates and removes the virus before it can be activated.
2. Because the number of viruses is increasing all the time, it is important to keep anti-virus software up to date with information on newly identified viruses. Anti-virus software vendors are constantly updating their databases of information on viruses and making this information available to their customers via their web sites or email.
3. Do not open email from unknown recipients or messages that contain unexpected attachments. A user should delete these types of messages. As a general rule, a user should scan every email attachment for viruses before opening it—even an expected attachment—as the sender may have unknowingly sent an infected file.