Email Address Harvesting and
the Effectiveness of Anti-Spam Filters
A Report by the Federal Trade Commission’s Division of Marketing Practices
November 2005
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I. Overview
This report describes the results of a Federal Trade Commission (“FTC”) staff study of
three aspects of spam in the current Internet environment. First, the study explored the current
state of email address harvesting – the automated collection of email addresses from public
areas of the Internet. The study found that addresses posted on websites were at risk of being
harvested by spammers, but that addresses posted in chat rooms, message boards, USENET
groups and weblogs (“blogs”) were far less likely to be harvested. Indeed, some chat room
operators took proactive measures to prevent the harvesting of email addresses posted by FTC
staff.
Second, the study explored the effectiveness of spam filtering by Internet Service Providers
(“ISPs”). The study showed that the anti-spam filters utilized by two free web-based ISPs
effectively blocked the vast majority of spam sent to harvested addresses. The implication
of this finding is that ISP spam filtering technologies are substantially reducing the burden of
spam on consumers. Nevertheless, spam sent to harvested addresses imposes costs on ISPs
receiving the spam.
Third, the study measured the effectiveness of using “masked” email addresses as a
possible technique in preventing harvesting. The “masking” of an email address involves
altering the appearance of an email address so that it is understandable by a person who sees
the address, but less likely to be discernable by automated harvesting software. For example,
to mask an unmasked email address such as “johndoe@ftc.gov,” the words “at” and “dot” can
be written out, and segments of the email address can be separated by spaces. The masked
version of the address would appear as “johndoe at ftc dot gov.” The study found that the
“masking” of an email address was very effective in thwarting harvesting.
II. Background
A 2