0 a computer program that collects email addresses from the internet in order to send spam (= unwanted emails) to them --
Some of these links may contain code to track the spambot's identity so that if a sale goes through then the spammer behind the spambot can collect a commission.
Since most spambot scripts use a fake e-mail address when posting, any email confirmation request is unlikely to be successfully routed to them.
Alternatively, the spam links are posted in the user's signature, in which case the spambot will never post.
Spambots usually create fake accounts and send spam using them, although in many cases it would be obvious that a spambot is sending it.