A computer virus is a form of malware. Some virus codes attach themselves to a program in the host computer. Viruses that can run independently are known as worms. A virus is either designed to compromise its host or to self-replicate to infect other computers.

Ref: http://www.messagelabs.com/threats

Spam is an unsolicited email. Spammers send out millions of identical emails, usually for financial gain. Spam has become increasingly sophisticated in order to avoid detection, with an increase in the use of malicious links, pdf, xls and mp3 spam.

Ref: http://www.messagelabs.com/threats

Phishing is a spamming technique used to trick victims into revealing confidential information such as bank details and passwords. Cyber-criminals mimic emails from reputable companies to lure victims to spoof websites where they are asked to input their personal details.

Ref: http://www.messagelabs.com/threats

Spyware is an application which sends the victim’s private information and web surfing habits to a cyber-criminal’s website. Spyware often installs itself without the user’s knowledge or explicit permission.

Ref: http://www.messagelabs.com/threats

A malicious link is a hypertext link that sends the user to a website. The site then infects the victim’s computer with malware. Using web links is a common technique because it avoids the use of malicious code within the email.

Ref: http://www.messagelabs.com/threats

Unlike viruses, trojans are self-contained programs which run independently. As the name suggests, trojans are disguised to be more destructive than they first seem. They can conceal malicious payloads which download confidential information for cyber-criminals.

Ref: http://www.messagelabs.com/threats