Hi Steve,
We have been dealing with a loot of this not only for DNNHero but for our clients at DeskPal.
Here is what I recommend for you:
1 - Download all your site files via FTP to your local computer;
2 - Using a program to do text search like NotePad++ or https://www.mythicsoft.com/agentransack - perform a search for .aspx or .asp file containing either "rootkit" or "Gönder" - These are terms found inside the files we have been finding. These hackers seem to like to advertise :)
3 - If you find any, there is a good indication that your site was hacked. If you don't find, I would perform another search just for .ASP or .PHP files. A normal DNN site shouldn't have either of these types of file extensions - If you find you may want to delete them;
That is what I recommend for now.
I hope it makes sense. This is what we have been doing.
Best regards,
Aderson