Repeated SQL Injection: Malicious Javascript in post_content column [ fix ]

Recently I’m dealing with a repeated contamination, having post_content column injected with malicious Javascript code ( wp_posts -> post_content ).
So far only two sites I manage are affected. Both are hosted by tsohost.com ( Paragon Internet Group Limited ).

After a Google search, I found out more sites with the exact same issue – all hosted by tsoHost.