lots of my websites got malware code in all files. But I actually have a backup of that site as a very old version. I can not update everything because there might have a lot of problems will happen.
1/ I install old site version on local, and manually copy folder wp-admin, wp-include, plugins, theme.. everything from old to new site except child-theme. (this is a fastest way but I don't know there's any risk)?
2/ I backup old site completely and start working again (it will take a lot of time)
I can not freely try each way because although the site has problem, its displaying on server now and I am must not doing anything wrong or they are gonna kill me & they kill me hard. So please advice me if the first way is ok to do?? Thank you very much.