My website had hacked Request for Assistance with Website Security and 404 Errors

Question

Request for Assistance with Website Security and 404 Errors

My website was hacked, and I have deleted suspicious files, changed the password, and removed fake users. However, I am still unsure if the threat is completely gone. Additionally, the number of 404 errors has increased to over 5350 pages.
 

I need your assistance with:

1. Ensuring the complete security of the website.
2. Handling the large number of 404 errors.
3. Improving the site's re-indexing and performance in search engines.

I appreciate your guidance and advice on these matters.

Thank you for your help.

Comments

Any insight on how you think the site was hacked? Where were the suspicious files? Do you feel this was a server issue, or Q2A code issue?

This information will help the community.

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"I think it is due to third-party plugins and themes because I recently experimented with some free templates."

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Why No One Help?????