[TezzellEnt]

Typically these advertisements find their way onto a site through vulnerable plugins. To minimize this, you can install the Wordfence Plugin and it will email you when to update. Another good plugin is rename-wp-login.php which will move the site.com/wp-login/ to site.com/somethingDifficultToGuess and have Wordfence not cache and robots not index that page.

[billmalarky]

I have basic auth protecting login and no plugins installed because I know they are usually the source of vulnerabilities.