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Short for Directory Harvest Attack, DHA is a type of malicious Internet attack where online spammers collect valid e-mail address and target those addresses in a spam attack or sell the lists of valid e-mail addresses to unscrupulous marketers. In a DHA attack, the spammer will select a domain name, for example, Webopedia.com. The spammer then sends an e-mail to any possible addresses within that domain name. If the e-mail server doe not reject the e-mail, the spammer knows it is a valid e-mail address and adds it to his target list.

See grabber.
See also "Getting Rid of Spam" and "All About Spam, Spim and Spit" in the Did You Know section of Webopedia.

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