It has been known for some unscrupulous Internet service providers to rent out their customer list to earn extra income, but it probably doesn’t happens much these days due to [...]]]> Conventionally, spammers obtain e-mail addresses from public sources such as newsgroups; forums, or the “TO:” and “CC:” lines of e-mail messages with an extensive circulation.

It has been known for some unscrupulous Internet service providers to rent out their customer list to earn extra income, but it probably doesn’t happens much these days due to the increasingly restrictive “anti-spam” legislations.

However, would you believe that there is a way for spammers to get your e-mail address – even if you’ve never, ever, used it.

It is called a “dictionary harvest attack” where legitimate e-mail addresses are found by brute force; guessing valid e-mail addresses at a domain using different permutations of common usernames.

The most targeted technique is to create a list that combines common first name and surnames and initials. For example jdoe@example.com, johnd@example.com, or johndoe@example.com.  For each message the example.com mail system will either accept the message, which means the address is valid, or decline it with an “invalid mailbox” message, which means that address is discarded.

If you have your own e-mail domain, and you have a “catch-all” account for unallocated addresses, then you’ve probably seen spam addressed to “webmaster@” or “manager@” for example.

The larger e-mail providers are aware of this and battle against these attacks.  Computers that attempt to send out multiple messages with such a pattern should be blocked; but it is very difficult for computer systems to differentiate between a dictionary harvest attack and other, genuine, high-volume mailings such as e-mail newsletters.

Terence Kierans CAVB (Certified Australian Virtual Business)
Principal, Cyberspace Virtual Services, Western Australia
www.virtualservices.com.au – Experience the Difference
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