The FTC set up 150 email accounts, 50 with an ISP that did not use a spam filter and 100 with two ISPs that did. These addresses were then posted on 50 websites, including message boards, blogs, chat rooms, and USENET groups where spammers might go to attempt to harvest the addresses.
After a five-week trial, email addresses at the unfiltered ISP had received a total of 8,885 spam messages, compared to 1,208 and 422 spam messages at the filtered accounts, effectiveness rates of 86.4 and 95.2 per cent.
The study concluded that spammers continue to harvest email addresses posted on websites, but addresses posted in chat rooms, message boards, USENET groups, and blogs were unlikely to be harvested.
“Indeed, some chat room operators took proactive measures to prevent the harvesting of email addresses posted by the FTC staff,” the study says.
More surprising was the effectiveness of 'masking', posting an email address that is understandable to a human but unreadable to software designed to harvest such addresses. A common form is to write an email address such as joebloggs@gmail.com as joebloggsatgmailcom.
After five weeks, unmasked email addresses posted up had received more than 6,400 pieces of spam, while the masked email addresses had received only one piece of spam.