A Directory Harvest Attack or DHA is a technique used by spammers in an attempt to find e-mail addresses. It is usually carried out by generating a flood of messages to multiple addresses at a mail server that is known to be valid. Most often, these attacks are targeted at corporations since they are likely to have a standard format for official e-mail aliases (i.e. jdoe(at) company.com, johnd(at)company.com, or johndoe(at)company.com).