• Adware
  Programs that secretly gather personal information through the Internet and relay it back to another computer, generally for advertising purposes. This is often accomplished by tracking information related to Internet browser usage or habits.
  
  Adware can be downloaded from Web sites (typically in shareware or freeware), email messages, and instant messengers. A user may unknowingly trigger adware by accepting an End User License Agreement from a software program linked to the adware.
• Dialers
  Programs that use a system, without your permission or knowledge, to dial out through the Internet to a 900 number or FTP site, typically to accrue charges.
• Hack Tools
  Tools used by a hacker to gain unauthorized access to your computer. One example of a hack tool is a keystroke logger -- a program that tracks and records individual keystrokes and can send this information back to the hacker.
• Hoax
  Usually an email that gets mailed in chain letter fashion describing some devastating, highly unlikely type of virus. Hoaxes are detectable as having no file attachment, no reference to a third party who can validate the claim, and by the general tone of the message.
• Joke Programs
  Programs that change or interrupt the normal behavior of your computer, creating a general distraction or nuisance. Harmless programs that cause various benign activities to display on your computer (for example, an unexpected screen saver).
• Phishing
  Phishing is essentially an online con game and phishers are nothing more than tech-savvy con artists and identify thieves. They use SPAM, malicious Web sites, email messages and instant messages to trick people into divulging sensitive information, such as bank and credit card accounts.
• Remote Access
  Programs that allow another computer to gain information or to attack or alter your computer, usually over the Internet. Remote access programs detected in virus scans may be recognizable commercial software, which are brought to the user's attention during the scan.
• Scam
  A fraudulent business scheme to gather information. In some cases a scam will ask the user install or use a service by misconception. Often a scam is based on ‘looking’ legitimate.
• Spyware
  Stand-alone programs that can secretly monitor system activity. These may detect passwords or other confidential information and transmit them to another computer.
  
  Spyware can be downloaded from Web sites (typically in shareware or freeware), email messages, and instant messengers. A user may unknowingly trigger spyware by accepting an End User License Agreement from a software program linked to the spyware.
• Spam
  Electronic junk mail. Sometimes spam is defined as any unsolicited email. A narrower definition is unsolicited advertising, most commonly for credit cards, weight loss methods, and pyramid schemes, sent to a mailing list or newsgroup.
• Spoofing
  E-mail spoofing is the practice of changing your name in email so that it looks like the email came from somewhere or someone else. Spoofing is generally used by spammers as a first defense against people finding out who they are. It's also used by general malcontents to practice mischievous and malicious behavior.
  
  
• Trojan Horse
  A program that neither replicates nor copies itself, but causes damage or compromises the security of the computer. Typically, an individual emails a Trojan Horse to you-it does not email itself-and it may arrive in the form of a joke program or software of some sort.
• Virus
  A program or code that replicates; that is, infects another program, boot sector, partition sector, or document that supports macros, by inserting itself or attaching itself to that medium. Most viruses only replicate, though, many do a large amount of damage as well.
• Worm
  A program that makes copies of itself; for example, from one disk drive to another, or by copying itself using email or another transport mechanism. The worm may do damage and compromise the security of the computer. It may arrive in the form of a joke program or software of some sort.

(Definitions for ‘Threat Types’ are provided by Symantec. http://securityresponse.symantec.com/avcenter/glossary/index.html)