WordPress Website Hacked. Hosting to blame?

As requested, this is now a new post.
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Yesterday, an Iframe banner promoting various websites appeared on my wordpress installs.

I’ve tried just about anything. After further examination, 11 website in total are compromised — all on the same hosting server. I’ve tried restoring from backups (with changes passwords to all accounts), and even then the iframe returned. Only one remained clean and that one has been down for several weeks now.

I formated my computer to ensure it is clean from ANY malware, and in its fresh state repeated the above process and still it came back (password changed once more).

Eventually I tried the hosting script installer with a fresh version, and even with an empty and fresh, updated wordpress, the iframe is still there! The only conclusion I see is that the hosting has been compromised. Anything can think of any other option?

I am now trying to import my backups to a different hosting server and then i’ll run a malware scan on it again in hopes that will resolve the problem.