Hi,
if you think, suspect or believe that you are hacked, do the following:
1. zip your entire osclass directory, all the files, everything, from the cPanel's file manager
2. export your database
3. if you have backups, go to your cPanel > backups and try to download version that was fine.
Now, send all those files (rename them accordingly) or upload them somewhere and share the links with Osclass Team: sistemas @ osclass.org
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Now, try to recall your steps, what you did, maybe installed some plugin? Unintentionally changed something? I know it's low probability, but just to make it sure.
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Regards
dev101