How to remove Sketch Theme permanently

I’m sorry but it sounds like your site has been hacked. You need to start working your way through these resources:
https://codex.www.ads-software.com/FAQ_My_site_was_hacked
https://www.ads-software.com/support/topic/268083#post-1065779
https://smackdown.blogsblogsblogs.com/2008/06/24/how-to-completely-clean-your-hacked-wordpress-installation/
https://ottopress.com/2009/hacked-wordpress-backdoors/

Anything less will probably result in the hacker walking straight back into your site again.

Additional Resources:
Hardening WordPress
https://sitecheck.sucuri.net/scanner/
https://www.unmaskparasites.com/
https://blog.sucuri.net/2012/03/wordpress-understanding-its-true-vulnerability.html

Hi.
We have the same kind of attack.

After brute-forcing their way in (we had a user with administrator role and a weak password) the hacker/robot filled our folders with malicious files. They seem to do that by first installing the Sketch theme, then using the 404.php of this theme to POST base64 encoded files.

We now have reinstalled clean backups of the site, hardened the security a little bit, and – of course – changed all the password with strong ones. They still try to get access to the site, but so far they did not succeed. We created an empty sketch folder in themes and put a fake 404.php in it to log the calls to that file – that’s how we know what the bad robot is trying to post.

Our question is: is there a place to report this kind of details?

Thanks.

Hello everyone,
I have the same problem. I wanted to know how you have improved security to prevent this attack. And ‘the third time that my site is attacked and do not know what to do.
Thank you