Often it happens that you open a new e-mail address and within days you start to receive spam. This can be very frustrating because you know that you haven’t given your e-mail address to anyone. How then did the spammers find you?

The answer to this question is the Directory Harvest Attack (DHA). This is actually an attempt to find working e-mail addresses which belong to an e-mail server. There are two different methods of finding a working e-mail. The first method uses the clean brute force of algorithm; therefore it checks all possible alphanumeric combinations of signs. The other is a more selective method which uses possible combinations of standard first and last names. For example: the spammer can easily obtain most of the first and last names that are being used and then he makes combinations. Let’s say he wants to send an e-mail to Bill Gates. He will then make combinations of that first and last name on an e-mail server. Therefore: bgates@, bill.gates@, billgates@, gates.bill@, etc… These methods work because there is a NDR (non-delivery report), or a report on the delivery of a message to the recipient, on almost all e-mail servers.

Various spam filters and other solutions on e-mail services usually efficiently take care of spam, but it is clear that as long there are computers, there will be spam.

Tags | E-Mail, Howto, Internet, Security, Tutorials