In their simplest form, e-mail harvester bots are simple programs that look at websites trying to pick out e-mail addresses.
Usually, the code that generates e-mail addresses on websites follow a very specific format: <a href="mailto:user@domain.com">E-mail me</a>. By picking out this code, it's easy for a bot to find an e-mail address on a website.
The issue that makes e-mail harvester bots such a threat is that they don't just look at one website - they have the ability to look through many, many websites all at once. A spammer instructs a harvester bot on a few search terms that identify their target market. For example, "computers" or "internet" could be good search terms. The harvester bot would then go and search a major search engine (such as google) for these terms. Google would return a list of pages that match those terms to the harvester bot.
Now that the e-mail harvester bot has a list of pages to analyze, it "visits" those pages and picks out all the e-mail addresses. As if that isn't bad enough, the typical e-mail harvester bot will also look for all the links on each of the pages, follow the links, and look for even more e-mail addresses and links! By searching for just a few terms, the e-mail harvester bot could look through many thousands - even millions of web sites, and get millions of current e-mail addresses.
MailMask.net protects against harvester bots by getting rid of the usual code used for e-mail addresses. Additionally, if the harvester bot does follow the link to the MailMask.net website, it won't be able to correctly answer the question we ask it.