Site hacked via this plugin

A relatively comment event. Hacker likely gained access to your FTP account and uploaded the files or used your Admin password to add their own plugins.

Changing password for everything would be my first thing to do.

As a side note, the poor rating of this plugin may be a good lesson learned as well.

What a coincidence, happened here too. I work in IT and know for a fact that these things may happen. But as a developer it is very irresponsible on your part to answer and just say “these things happen” and not even take a look at your own files. I will make sure my client does not install any more suspicious plugins without the proper research in the future, but at the same time YOU as the developer should take a look at your own code.