On Christmas Eve day, several of my sites were 'visited' by what I presume to be a bot, all from the same source IP address.
The attack consisted of attempts to register many new user accounts, each having a username containing the term 'DVD':
Soccer DVD, DVD Immature, Underworld DVD, Adult DVD, Enigma DVD, DVD shrink, Blues DVD, Trick DVD, Portable DVD Player, DVD Decryptor, Federation DVD
The email addresses were all unique of course - since the bot attempted to register multiple user names on each site. The sites were configured to include a text field user profile, so that users can share interests, etc.
The spam bots were stuffing URLs and text ads for DVDs into the profile fields, in an attempt to generate search engine "link love", or so it appears.