I agree with Bruce and suggest you check your IIS logs to see what urls are being called.

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Willem,

I don't think it is fixed by the core. There are several things you can do against the spam registrations:

1) Turn off the copyright comment in your host settings (I don't know if this helps, but it can't be wrong)
2) Do not use "public" registrations (at least verified)
3) Create a custom registration page and block the default registration page: http://www.dnnsoftware.com/wiki/page/...
4) In addition to 3) you should upgrade DNN to 7.2.2 or higher as the bot is able to register using ctl=register despite the HTTP 404 error message
5) Use reCaptcha (as you said) - there is a module for this: http://www.interactivewebs.com/blog/i...

Best wishes
Michael

PS: You may read my blog article in the German Usergroup (http://www.dnn-usergroup.de/Community...) if you understand German (or use Google to translate:-))

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You can also try using the reCaptcha option for stopping the spam registrations. reCaptcha is a smart initiative by Google. You can stop all the spam registration by utilizing reCaptcha.

 

Here at InteractiveWebs, we decided that we would enable Recapcha (a cleaver Google Initiative https://www.google.com/recaptcha/ ) that is harder to be machine broken, and test the results. We found that all the spam registrations stopped once Recaptcha was used.