411 REFERENCE · Wikibooks
CAPTCHA/Usages
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
User X wants to send email to Y. They go to example.com/mail.php and notice some words. The form says that he has had over 100 spam emails sent via the form.
Spammer S edits a page on wiki W. The wiki had been spammed before. They notice that the page is not saved with their spamming software.