If you operate a content management systems (CMS), you're probably familiar with the curse of botnet attacks on the user registration and persistent spammers on comments. These are IP address that are attached to your CMS from China, i.e. the 163.com domain, sending regular, daily spam message updates about Viagra, Cialis, and faux haute couture, sometimes for years on end. Or they continuously try to attack the user registration CAPTCHA, trying to create accounts to do the same or worse, sometimes using inane responses to the CAPTCHA like "TooBad1" through "TooBad257", not really doing any damage but consuming sometimes scarce resources and filling up the logs (to mask other activity sometimes, like database attacks).
This is not a problem specific to any one CMS, and will happen to Drupal, Wordpress, or Joomla. Drupal, however, logs the events as part of core functionality, allowing them to be noticed by the operator. Having dealt with it for well over a year, mostly manually, I found two great modules in the Dupal repository