Computer viruses are small programs that, when activated by a computer user, attack their host files. A virus can corrupt, destroy or delete a file, or make it otherwise unusable. Much like flu viruses, a computer virus can spread reproduce rapidly, mutate and cause considerable harm. These viruses spread through a host like e-mail, CD or a file on the internet. Moreover “.zip” files are also found as the source to conceal viruses and used as a transmission medium for high percentage of new viruses.

Many users open and start file attachments from unknown external senders due to which the user not only infects his or her PC, but also allows the virus to spread throughout the network of computers. In 2004, the Information Technology Management Security reacted to the ongoing problem of viruses received at many corporate offices by implementing measures to block attachments received in e-mails from external sources, including .zip files and “.exe” and “.bat” attachments. By continually blocking these types of files, the company is protected from new viruses yet to be defined.
A worm is a destructive program which can independently spread throughout a network in order to damage and crawl as many systems and networks as possible. One of these destructive program is Trojan.

The term spyware refers to programs that spys on a user’s activities while they are on the internet. Spyware is mostly found hidden in downloadable programs, where it installs itself onto the user’s PC without his or her knowledge and then monitors or analyzes the user’s activities for advertising purposes (adware). The far more dangerous form of spyware is known as keyloggers which capture the user’s keystrokes to include in formation on accessed data.

Dialer is a term that refers to a program that dials a telephone number to set up an additional Internet access on a computer and can independently dialup an access number. The access number a dialer uses to do this determines the cost of the connection. Once installed, the dialer can dial up expensive internet connections and invoice the computer user for the charges. Illegal use of dialers has been increasing in recent years, since they can be installed on a computer through fraudulent advertisements, insufficient background information or technical tricks, without the computer having expressly or fully authorized the installation.

The Trojan Horse , called as Trojan for short refers to the conquest of the ancient city of Troy using a clever tactic-the Trojan Horse. The Greeks built a wooden horse, concealed warriors in the hollow belly of the figure and gave as a present to the city of Troy. The sudden attack from within their own city walls caught the Trojans by surprise, and the city fell to the Greeks. Trojans in the Information Technology world use essentially the same principal. It is a program designed to do damage. It is concealed in seemingly helpful applications and executable files. When installed, it hides in a computer’s files. Here, it can install other destructive programs on the computer or log information including passwords and other information data stored on the computer, and send it to the internet vie the internet to the party who initiated the Trojan.

News fabrications are known today as also reports or hoaxes. In the field of electronic communication, hoaxes are false e-mail reports or e-mail chain letters. Such e-mail hoaxes contain fake virus warnings, letters of congratulations, petitions, or calls for donation aiming to exploit the recipient’s generosity or kindheartedness. The e-mails are designed to entice the recipient to forward the chain letters to all of his or her friends and acquaintances. Closely related to the e-mails hoax is the e-mail scam. Moreover, phishing and spamming are also used extensively.

Malicious Code is any kind of computer program designed to cause damage. Attackers employ such programs on the Internet to damage or inhibit the computers or software of other users.

Now a days, few programs with malicious code can be assigned to only one clearly defined category which posses the worst characteristics of viruses, worms and Trojans. They all are products of highly sophisticated hacker methods. As a result, additional Trojans hidden in worms and phishing e-mails can contain spyware. Such combined forms are also called hybrids or blended threats.

The term scam refers to a fraud in this context, fraud using mass e-mails. As a rule, Internet users receive an e-mail inviting them, under false pretenses, to take part in pyramid schemes or to perhaps pay an advance with the promise of financially tempting commissions or profits. To make these offers appear convincing and legitimate, Web sites are made to look virtually identical to those of public agencies or banks. One famous example for this is “Nigeria” scam. Some more are phishing and farming.

Phishing comes after combining the two words “password” and “fishing” which means objective to “fish for passwords”. Using an e-mail that appears legitimate, the person doing the fishing send a very authentic-looking message, usually from banks or other online payment systems to trick the recipient into divulging access data and passwords. If the data is provided by the recipient, the phisher, for example, can use the collected access data or passwords to transfer funds out of the victim’s accounts. Hoax, scam and spam are similar to phishing e-mails.

Pharming is related form of phishing. The word is derived from the words “farming” and “phishing”. Pharming involves manipulating the process of calling up a web site where an unsuspecting Internet user is directed to a forged site to gain access to the user’s passwords or other personal data. The forged pages are kept on the servers of the persons operating the pharming scams. Such people often operate very large farms for this reason.

• Never install or open programs or software that have not been authorized or certified.
• Never change the settings of an Internet Browser on a computer.
• When using Internet, it is important to have a healthy degree of skepticism when confronted with messages that call for "OK" confirmations, ask a user to give authorization by clicking on "Yes", or before accepting security queries.
• Never open attachments in e-mails from unknown senders.
• Never fulfill a chain letter request. Such e-mails should be deleted without further consideration.
• All e-mails that promise profits, commissions or high incomes should be deleted.
• Never reply e-mails that request for personal data.
• Internet users should always make note of the URL appearing in their brwoser's address line. The secure URL should begin with the characters "https://", which indicated the server storing the site in question must be authenticated with a browser certificate.