Unknown User Registered into my system
These are robot spam registrations. To my eye, they look like they originate from XRumer.  XRumer knows how to complete the registration process of LoginToboggan and knows how to solve simple CAPTCHAs, so these measures will not stop XRumer from registering.

The modules I've found to be most effective against robot spam registrations are MotherMayI and CAPTCHA Riddler.

Both these are based upon the same idea: To register, the registrant should be able to answer a simple question where the answer is obvious to a human, but not to a robot.

If you site's language is not English, almost any question will work, since robots do not have multi-language skills.

CAPTCHA Riddler lets you set up a "pool" of questions (so a returning robot will face a different question on each visit).  MotherMayI only allows one question, but let you set up an RegExp for the answer and also has allows for a longer text to "hint" to a human what is expected.  I currently prefer MotherMayI, but check out both.

PS: So far, no spam robot has managed to register at any of my 20 sites (all that accepts registrations by the public are protected by MotherMayI).