Who can access my account?

Just notice that something strange happened to my website. A new page was introduced without my permission. This page is a template for an “About us” page. The idea is not bad, but just wondering why this page will appear on my website without my pre-knowlege.

Not long ago, also received a spam message pretending they are from Wix.

Just wondering how I can stop this happened again.

Many Thanks in advance.