Selecting Preview while creating Blog Post redirects to a malicious site

Mac OSX 10.12.1
Chrome Version 54.0.2840.98 (64-bit)
WordPress 4.6.1
Theme Skillful

Beginning November 8, 2016

To reproduce:
1) WordPress Dashboard
2) Select Blog Posts > Add New
3) Create any text in new post (including title only)
4) Select Preview in the Publish box in the top, right-hand portion of the screen
5) Instead of seeing the Preview, I am getting redirected to a malicious Windows 10 key site

Steps taken to troubleshoot:
1) examined the Users and found an unknown user with administrator access – removed them
2) found references to the redirected site in the index.php as well as others (I don’t know what the others are, my web developer found them)

My web hosting service only keeps 24 hour backups, so they do not have the backups prior to the hack

My question – has anyone seen this before? How did you get back to whole?

Thank you.