Can I switch to Wordpress backup from FTP this way

[HappyS]

My current (addon domain) website WP installation is unusable due to hacker messed it up. Can I delete every file with the FTP client in its directory and replace it manually with backup files? Will it work?

P.S. I don't want to replace everything in the home FTP directory because there are more addon domains there!

 

[MrBlue]

Replacing your current WP install with a backup will work and may in fact correct your issue however there is more to consider when correcting a hacked WP site. For example your DB may contain the malicious code thus replacing files won't fix the situation or perhaps your FTP program is infected and is the root cause of your hacked WP install.

This may help you track down and resolve your issues: https://codex.wordpress.org/FAQ_My_site_was_hacked

 

[HappyS]

Replacing your current WP install with a backup will work and may in fact correct your issue however there is more to consider when correcting a hacked WP site. For example your DB may contain the malicious code thus replacing files won't fix the situation or perhaps your FTP program is infected and is the root cause of your hacked WP install.

This may help you track down and resolve your issues: https://codex.wordpress.org/FAQ_My_site_was_hacked

I think you are right two of my addon websites were target of the hack, and their folders are filled with trash htmls, while my main website's folder is clean. I think hacker didn't hack admin passwords but something else, because I used different passwords for every domain.