Hacker targets WordPress powered website. Reason is simple, it is very famous, opensource, vulnerable plugins and themes. Don’t be panic if you got hacked, because lots of defaced sites are marely done via inserting index.html or replacing index.php. So, most time database and original files are found safe.
So here you need to remove that malicious file. Most time it was index.html. However, remember to keep backup in safe side while using this process. As