I can confirm that this related to patching to 2.07 version and that the issue is resolved with the latest update as far as we can see.
We had to do full back-up restores, although so far as we could see the injection was into the file structure as opposed to the database.
I would urge anyone to update all their sites running QuadMenu to 2.07 immediately. The security backdoor can still be exploited even if the plugin is installed but deactivated.
A software update should suffice and mean no deactivation is necessary.
Hopefully, that helps anyone else reading this who has experienced this issue.
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This reply was modified 4 years ago by aewing2021.