E-mail addresses harvested from the public Web appear to have a relatively short "shelf life." When e-mail addresses we posted on the public Web were removed, there was a pronounced drop in the amount of spam they received each day. The change was not absolute—on a given day, an address might receive a few spam messages even months after it had been removed from the public Web. But such spam was on the order of 2 or 3 messages per day, compared to the thirty or more messages received by addresses still on the public Web.

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Obscuring an e-mail address is an effective way to avoid spam from harvesters on the Web or on USENET newsgroups. Even when posted in publicly accessible areas, none of the addresses we obscured—whether in English ("example at domain dot com") or in HTML—received a single piece of spam. Users who want to avoid spam should consider obscuring their addresses when possible.