someone using my ip-adress

Dear,

Could you help me with this? Since couple of weeks i noticed some suspicious activity on my site. There where alot of spambots getting true my security messures. Somehow the spambot/someone was able to create new spam groups in buddypress under the admin (my) name. Whenever i clicked on the image of the person who created the spam group it linked to my profile. I delete all spambots and spamgroups.
Then thankx to the instalation of the stop spammers plugin, I noticed some new suspicious activity. There was an user with my ip adress that was not anybody of my home that was trying to login my site. I don’t know if he succeed. The user try to do it many times a day. I have a security plugin that noticed me that a user with my ip but a diffrent weird non existing name failed to login. Am I hacked? How can anyone use my ipadress? Is it my router?
I saw stop spammers shows a log report: the user has no email adres.
even spam shows an email adres. the author has that weird non existing name. The script of the log report says wp-login.php.

Could anyone help me to interpetate this info and could anyone advise me what to do best?

thanx