According to the information provided in your comment I imagine this scenario: An attacker got access to your account brute forcing the login page or stealing your password in other ways. Then he/she entered in your site (which caused the plugin to send the alert of a successful login). Depending on the access level granted to the attacker he/she may have affected the configuration of the hosts file (only if your site is hosted in a private server) and that may be the cause of the issue with the “send_log” action (the could not resolve host issue).
This is hypothetical because there is no sufficient information to actually affirm that something like this happened.
If you still have access to the control panel of your site then you may want to block access to all IP addresses while you investigate the issue, that will stop the (supposed) attacker for some time. Then after you reset your WordPress user password, go to the “Post-Hack” page in the plugin and reset everything (from the security keys, to all user passwords), be sure that no new admin users were created during the (supposed) attack.
If you give me more information I can help you more. Good luck.
