an image, typically too small to be seen, which resides on a page or HTML e-mail of one site but is hosted on the server of a different site. These images allow one server to send information to another, or allow information about the page (e.g., that the email was viewed) to be recorded on the server.

a list of e-mail addresses, domains, or IP addresses which are banned from connecting to the server using the blacklist. See whitelist.

to return an e-mail as undeliverable; also, the undeliverable e-mail.

an anti-spam anti-virus technique that relies on challenging the requestor to prove he is not an automated process by responding to a puzzle, instructions, or deciphering text in an image.

the common name for malicious software distributed by email; often these are really trojan horses, relying on tricking the recipient into launching the executable code.

U.S. Federal law against junk e-mail behaviors.

malicious software. See: virus, trojan horse, worm, spy-ware.

a scam, typically over e-mail with a website component, where the attacker masquerades as a legitimate business that the recipient may have ties with, such as a credit card company; the emails appears to come from this company, and it uses legitimate logos, text, and links pointing to that company's website. Once the user follows a key link to a different website, the attacker asks for details such as passwords, PIN numbers, and credit card numbers in order to harvest them for malicious use.

software which delivers information to the user when the user requests, or pulls it from the server. The web is a pull technology.

software which delivers information to the user when the server initiates contact and transfers data to the client without the client acting in any way. E-mail is a push technology.

either a trademarked luncheon meat (Spam), or the common name for junk, unsolicited, or otherwise unwanted e-mail (spam), depending on capitalization.

software that scans and analyzes incoming e-mail, looking for patterns which may indicate it is spam; e-mail which is determined to be spam is either discarded or marked for later sorting. Spam filters on the client (e.g., in Outlook, Mozilla, Eudora, or Apple Mail) allow you to view the junked spam and discard it; spam filters that run on e-mail servers often hinder business uses of e-mail because the recipient is not made aware of the filtered e-mail, and the sender does not receive notice of a bounce.

malicious software which relies on the recipient performing some action (such as double-clicking or opening an attachment) in order to deliver its payload. Trojans are so named because they are often diguised as something the recipient may want to open. Distinct from worms (which do not require user intervention), and viruses (which attach themselves to legitimate software).

a list of e-mail addresses, domains, or IP addresses which are permitted to pass unhindered through any filter using the whitelist. See blacklist.