My site is hacked ?

I installed WordPress in my domain a few months ago. At first I wanted to use WordPress for all the applications but then I decided to use for my site Invision Power Community, do not to allow the registration of new members on the WordPress installation. and also to use Invision for forums, blogs and personal albums for my users. Now I use WordPress only for some plugins like CyberSeo and Advert, that I use without the need of registration, for all users. My problem is that for a couple of months, despite not having installed any plugins for the registration of new users, I’m witnessing the registration on my installation of WordPress of new users. In my site already have registered, without there being any plugin of registration a hundred of new users. I fear that this is a hacker, that did not notice that the installation of WordPress no longer contains the most important plugins such as forums and photo albums. How can new users register without the register plugin? The impression is also that every new user also register other users at once. This is the typical confirmation message of the registration sent to me in a unique email:

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Someone can help me ? How is possible that new users subscribe to my installation of WordPress without any registration plugin ?

• This topic was modified 5 years, 9 months ago by t-p.
• This topic was modified 5 years, 9 months ago by Jan Dembowski. Reason: Moved to Fixing WordPress, this is not an Everything else WordPress topic
• This topic was modified 5 years, 9 months ago by Jan Dembowski.