Botnet

Spambot

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A spambot is an automated computer program, or, more rarely, a script, designed to assist in the sending of spam.

E-mail spambots

E-mail spambots harvest e-mail addresses from the Internet in order to build mailing lists for sending unsolicited e-mail, also known as spam. Such spambots are web crawlers that can gather e-mail addresses from Web sites, newsgroups, special-interest group (SIG) postings, and chat-room conversations. Because e-mail addresses have a distinctive format, spambots are easy to write.

A number of programs and approaches have been devised to foil spambots. One such technique is known as address munging, in which an e-mail address is deliberately modified so that a human reader (and/or human-controlled Web browser) can decode it but spambots cannot. This has led to the evolution of more sophisticated spambots that are able to recover e-mail addresses from character strings that appear to be munged, or instead can render the text into a web browser and then scrape it for e-mail addresses. Alternative transparent techniques include displaying all or part of the e-mail address on a webpage as an image, a text logo shrunken to normal size using inline CSS, or as text with the order of characters jumbled and restoring the order using CSS, where users are then able to see the address.

E-mail blockers

The term spambot is sometimes used in reference to a program designed to prevent spam from reaching the subscribers of an Internet service provider (ISP). Such programs are more often called e-mail blockers or filters. Occasionally, such a blocker may inadvertently prevent a legitimate e-mail message from reaching a subscriber. This can be prevented by allowing each subscriber to generate a whitelist, or a list of specific e-mail addresses the blocker should let pass.

Forum spambots

Forum spambots surf the web, looking for guestbooks, wikis, blogs, forums and any other web forms to submit spam links to the web forms it finds. These spambots often use OCR technology to bypass CAPTCHAs present. Some spam messages are targeted towards readers and can involve techniques of target marketing or even phishing, making it hard to tell real posts from the bot generated ones. Not all of the spam posts are meant for the readers; some spam messages are simply hyperlinks intended to boost search engine ranking.

This category of spambots has gained considerable notoriety since November 2006, with the introduction of XRumer, a forum and wiki spambot which can often bypass many of the safeguards administrators use to reduce the amount of spam posted.

The easiest way to prevent spambots from posting on forums, wiki, guestbook, etc. is to enable e-mail activation by installing a mail server on the host (eg: Sendmail, Postfix, Exim.), since most spambot scripts use fake or randomly generated names on real e-mail providers, the e-mails will mostly never be successfully routed to them.

See also

• Address munging
• Botnet
• CAPTCHA
• E-mail address harvesting
• List poisoning
• Spamtrap
• Stopping e-mail abuse
• Spider trap

External links

Look up spambot in Wiktionary, the free dictionary.

• Stas Bekman's Article on Botnets and how they are used for spamming
• Botnet discussion mailing list
• Fight Spam - Join Byteplant's Spambot Honeypot Project
• Spambot Beware! - information on how to avoid, detect, and harass spambots
• Bot-trap - A Bad Web-Robot Blocker
• How to block spambots