Computer viruses are a security issue that users need to recognize and attempt to avoid. A computer virus is a program that infects data files or software programs with which it comes in contact. Because of this, viruses are often transmitted when you retrieve an in­fected file from secondary storage or by sharing infected files across a network. Other threats exist that can wreak havoc on your computer system or data.

A worm is a malicious, self-replicating program specifically designed to cause damage. Unlike a computer virus, however, a computer worm does not infect computer files to spread. In other words, worms affect the network whereas viruses typically affect computer files and data. A worm makes copies of itself and sends those copies to other computers through a network. The first worms were sent as email attachments. When an infected attachment was opened, the worm inflicted its damage and then sent copies of itself to other computers. Newer worms do not require any action by the users. Instead, the worm is activated when an email message is read or spreads itself automatically through the In­ternet. Unfortunately, worms are not limited to email programs alone. Worms can also be ac­quired though instant messaging programs, chat rooms, and shared network folders. Worms can delete files, transmit data, overload primary storage, or create a secret electronic entrance into a network.

Another computer threat is the Trojan horse.  A Trojan horse is malicious software designed to look like something useful. Trojan horses may appear to be useful or interesting programs (or at the very least harmless) to an unsuspecting user, but they are harmful when executed. Like virus­es, Trojan horses are most often spread through email attachments. Trojan horses can erase, cor­rupt, or overwrite data on a computer, upload and download files, log keystrokes for the pur­pose of stealing information (such as passwords), or allow remote access to a computer.

Other common types of viruses include:

• Macro viruses – executable functions inside programs. Duplicates through email attachments and can delete files
• File infecting viruses – erase the hard drive
• Script viruses – overwrite .jpg (picture files) and .mp3 files (music files)

Beware of the many emails that are circulating telling you that you are going to get or have got a virus.

An additional computer security threat appears in the form of unauthorized access. Although unauthorized access can take place in several ways, the most common type is per­petrated by a computer hacker or cracker.

A hacker is an individual who uses his or her computer know­ledge to break into personal or business com­puter systems to delete, steal, or alter files. The motivation for hacking is to steal information, sabotage a computer, or perform some other type of illegal act. Hacking is a crime and the government has authority to prosecute individuals participating in hacking activities and increases the penalties for this crime.  In general, hackers gain entry to computer systems simply to find out how they work and the perpetrator gains personal satisfaction from knowing that he fooled the system.  It relatively seldom happens that a hacker damages the system and often plants a ‘flag’ in the computer system to show that he had been there.

Crackers are perpetrators who do not simply intend to gain entry to a computer system, but have ulterior motives when accessing the online system.  These perpetrators will bring a computer system to a grinding halt or will make copies of sensitive information for use in an unlawful manner.